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FEMA To Use Cell Phone Signals To Find Survivors 286

Posted by timothy from the safety-tech dept.
twistah writes: "CNN had an interview with a representative of the Federal Emergency Management Agency (FEMA), the agency helping with the New York WTC rescue effort, who said that Lucent has given them technology to trace the signal of cell phones. The idea is that people will give them phone numbers of cell phones and pagers of people missing due to the WTC collapse, which FEMA will call and attempt to trace the signal to find the missing people. FEMA has now put this information on their web site, and are dubbing it the 'Wireless Emergency Response Team.'"
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FEMA To Use Cell Phone Signals To Find Survivors More

FEMA To Use Cell Phone Signals To Find Survivors

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  • Can people live this long under rubble? Or are they just finding bodies like this?
    • Is that really viable at this point? Most cell phone batteries don't last for too many days, even while not in use. They'd last even less time if the owners were trying to use them to call for help like some of them did. Unfortunately most probably didn't get through because of the phone network jam that happened right afterwards...

    • Re:Are they alive? (Score:3, Interesting)

      by spudnic ( 32107 )
      I heard reports that there where several subteranian areas that have pockets that are open. This was followed up by saying that there where a lot of snack shops and the such that would have been stocked with food and drinks.

      If someone was lucky enough to find themselves in this situation they could survive for quite awhile.

      • Yeah, I guess if a building fell on me, I'd want to be in a snack shop. Seems so unlikely, though
        • If I understand correctly, there was a huge shopping area or something underneath the towers. I'm sure food would not be hard to find in that situation.

          • Re:Are they alive? (Score:2, Informative)

            by humblecoder ( 472099 )
            If I understand correctly, there was a huge shopping area or something underneath the towers. I'm sure food would not be hard to find in that situation.

            Yes, there is a shopping mall below the WTC complex, as well as a PATH station and a NYC Subway station. I haven't heard anything on the news about how it held up under the weight of the collapse. It would seem that if it did hold, rescue workers could approach the site from below via the train tubes.

            • Re:Are they alive? (Score:4, Informative)

              by Rackemup ( 160230 ) on Saturday September 15, 2001 @07:23PM (#2304264) Homepage
              They're trying to clear the subway tunnel under the building to see if anyone actually on the platform under the towers survived. The problem is that water mains have burst, flooding the tunnels and filling them with debris. At present I think they're a third of the way there.
      • Perhaps, but there's another problem: air. You'd need a hole somewhere, or some sort of ventilation, or they'd have asphyxated by now.
    • I do hate to say this, but a travisty of this magnitute will have some positive outcomes. Weither it be search and resuce tech and procedure, building arcitecture, or just plain people looking over their shoulder, this was necessacary for humanity to experience even though it blows. Look at the Titanic. Because of that, regulations were created to make sea travel safe.
  • I work as a co-op for the Mitre Corporation [www.mitre.org] and last week it was announced on a company email list that about a dozen MITREites are down in NYC helping find people with this cell phone technology. Details have been a little sketchy as to precisely what was being used and such, so it's nice to get that information. I'm really proud to be part of a company doing what we can to help.

  • Wont the phone batterys be dead by now? (Score:2, Interesting)

    by Anonymous Coward
    I was thinking about this the other day, but if people were frantically calling these cellphones then the battery would almost certainly be dead by now, and even if this were not the case my phone will only last about 4 days without getting charged as it would ramp up the power output to try and get a signal.

    Hopefully this will be a good launching point for this technology in the future
    • well, when my cellphone has a signal it will last a little longer then a week, when there is no signal it actualy uses less power. After 15 minutes with out a signal the phone begins to rest and conserve power, it will check for a signal every once and a while and will actualy use less power then when it does have a signal.

  • GPS equipment in phones would be useful here (Score:3, Interesting)

    by smoondog ( 85133 ) on Saturday September 15, 2001 @05:36PM (#2304004)
    For safety reasons cell phones are going to have GPS receivers in them soon to tell 911 operators where you are when calling on your cell phone. This would be totally useful here, because there are going to be a lot more cell phones in that pile of rubble than living people. While I agree with the privacy concerns (including my own) this would have been totally helpful here. (Especially since most cellphones don't have more than 3-5 days of battery life. They should all be running down by now).

    -Sean

    • Re:GPS equipment in phones would be useful here (Score:4, Insightful)

      by Russ Steffen ( 263 ) on Saturday September 15, 2001 @05:42PM (#2304026) Homepage

      Actually, it would be nearly useless in this case. GPS signals are very, very weak and can blocked by as little as a sheet of aluminum foil or a few millimeters of water. A GPS receiver under all those tons of concrete and steel would never be able to aquire and track.

      • Actually, it would be nearly useless in this case. GPS signals are very, very weak and can blocked by as little as a sheet of aluminum foil or a few millimeters of water. A GPS receiver under all those tons of concrete and steel would never be able to aquire and track.

        No problem; just cache the result if you lose the GPS signal. In cases such as this, your location wouldn't change too much, and people could use the last-known location information as a starting point for exhaustive searches.

        • Re:GPS equipment in phones would be useful here (Score:4, Insightful)

          by Russ Steffen ( 263 ) on Saturday September 15, 2001 @06:08PM (#2304105) Homepage

          Except in this case the location cached before the collision would be something like "1 World Trade Center, NE corner, floor 45 through 55". (GPS's vertical accuracy is much worse than it's horizontal accuracy.) Now add the fact that the nearest cell tower was on the roof, and it went offline immediately after the collision. Now add the fact that floors 45 through 55 are now laying in a pile with the other 100 floors. That cached position will likely be hundreds of feet from where the phone ended up - and that's assuming the person and phone ended up in the same place.


          I'm not saying that GPS in cells phones is or isn't a good idea. All I'm saying is that it wouldn't be likely to have helped locate anyone in this case. The only way to find and rescue the people with those cell phones is to trianglate the signals from the phones.

        • No problem; just cache the result if you lose the GPS signal

          Sorry, but you're way off base here. Try walking around a major city center with a handheld GPS sometime. The cached location would probably show that the phone was somewhere else entirely - perhaps in the street approaching the WTC, or even at a suburban train station or bridge where the sky was less obstructed.

    • No, GPS doesn't work without line-of-sight to the satellites (and you have to have 3-4 satellites at a minimum, which is tricky even outdoors in a place like Manhattan).

      But having the cell triangulation that is (i think) being mandated for general emergency services use would be useful in this situation. it proovides effectively the same results but only works in a cellular-enabled area...
      • They could put local GPS broadcaster to send a stronger signal and help provide more accurate locations. This was suggested for a airline auto-landing system using GPS at one point.

        That being said, it is still highly unlikely that the signals could get very far through the structural debris.

        It is worth trying for the chance that they can connect to someone alive, in an air pocket, or perhaps just to expediate the location and removal of bodies in the rubble. It might also help in the identification of bodies too.

        • one of the fundamental problems is that it doesn't work in buildings AT ALL... it's absolutely horrible... now add in the resolution that it offers +/- 10 meters.. now add in multiple ones that could be close together... it'd be a mess and wouldn't result in anything anyway...
      • Question - why use GPS at all? I'm sure that at any given location a mobile phone is in touch with more than one mobile transmitter within reach. Why could these not be adapted to triangulate the position of a mobile?
    • I believe the technology they are implementing in the 911 system will allow operators to triangulate the cell signals to determine the callers location... not really a GPS system since GPS can't be used inside (or under millions of tonnes of rubble).

      Isn't it also possible to use sensitive electronic equipment to pick up the "here I am" signal that cell phones send out periodically to the towers?

      • Isn't it also possible to use sensitive electronic equipment to pick up the "here I am" signal that cell phones send out periodically to the towers?

        Even simpler you put a cellular base station onto a truck then you can not only pick up the registration you can also call the phone.
    • Even if GPS were to work in a place like that, I think that firstly the accuracy is not high enough to find out exactly under which piece of debris a person is hidden, and secondly GPS will not tell you how deep a person lies.
    • A receiver would only tell the cell phone carrier where they were, it wouldn't tell the person on the other end of the line where they were.

      With the current situation this would do no good. The survivors already know they are under a pile of rubble. GPS won't shed any new light for them.

  • batteries are dead by now (Score:3, Insightful)

    by bjtuna ( 70129 ) <<brian> <at> <intercarve.net>> on Saturday September 15, 2001 @05:36PM (#2304005) Homepage
    by now, any of those ppls' cell phone batteries have long since worn out.
    • Comment removed based on user account deletion

    • While you're almost certainly correct about phones, my two-way pager's battery lasts for at least a month, so there's at least that.

    • My phone's [motorola.com] batteries typically last over a week even when I leave it on all week long, but then, battery life was one of my main concerns when I was looking for a phone.
      • My phone's [motorola.com] batteries typically last over a week even when I leave it on all week long, but then, battery life was one of my main concerns when I was looking for a phone.

        One of the main factors affecting battery life is TX power. If you are always in an area of good coverage then it will never use maximum power.
        The situation the phones in question have been subjected to was progressive loss of nearby cells, WTC1, WTC2, South Manhattan. Combined with attenuation of signal.
        A phone which would usually last a week might not last 8 hours taken somewhere where no base station was available.
      • Battery life is highly variable, and dependent on signal strength and talk time versus idle time. For example, my cell phone has a claimed battery life of 5 days. If I spent all my time right at the base of a cell tower, it would last that long. However, I spend much of my time working in a large building that blocks cell-phone signals. The phone responds by raising its power levels to compensate. I'm lucky to get two days of battery life. Most of these cell phones are buried under tons of steel & concrete. The phones will either use their batteries quickly, or go into a power saving mode where it shuts off its receiver entirely until the user presses a button. In either case, they're not listening & not transmitting, and not much use to the rescuers.
        • Most of these cell phones are buried under tons of steel & concrete.

          Also what are they going to be communicating with? Have rescuers brought in truck mounted cell sites or was power restored to adjacent sites in short order? (Though if they only had a land line connection to the switching centre underneath the rubble that wouldn't help much.)
    • If Id be stucked under I'd contact in intervals of hours, I wouldn't leave it on all the time to try to save some battery time. I'm sure some of them thought about that issue.

  • E911 (Score:1)

    by Anonymous Coward


    there is a blurb at techienews here [utropicmedia.com] about E911 with a link to an article about when phone companies were supposed to have it.

  • Cellphone batteries running out? (Score:3, Interesting)

    by zulux ( 112259 ) on Saturday September 15, 2001 @05:37PM (#2304009) Homepage Journal
    After so many hours, woulden't most cell phone batteries have run out by now. I hope I'm wrong.
    • It seems to me that there are two ways for cell phone signals to be useful so long after these phones' last charge :

      Someone with a very big clue realizes cell phone signals will be useful when rescue operations take place and convinces all the cell phone companies to shut down all the cell towers around the area of the disaster. That way, cell phones don't get any signal anymore and stop "talking" to the towers, therefore conserving battery energy. Afterward, during the rescue operations (now), cell towers are switched back on for a few minutes every 2 hours or so, and rescuers take advantage of these few minutes to scan the area for cell phone responses.

      Buried victims who are still alive *and* still able to reach their cell phones *and* still able to think clearly enough realize that their cell phones may be useful to their future rescue, switch them off, then turn them on only a few minutes per day, to make a call, or hoping that someone will pick up their phones' signals.

      These are the only two possibilities I can think of that would keep cell phones alive and somewhat usable so long after the tragedy. Sadly, I don't think either possibility is even remotely likely. Of course, I wish with all my heart that I'm wrong, and also that battery technology and power management are now advanced enough that lifes can be saved as a result.

      • As I understand it - if a Cell phone can't get a signal, it boosts it's power output in an attempt to connect. We have a tower near my house, and the my cell phone stays on standby for six days - if I bring it backpacking and leave it on, it's dead within hours. You idead is good though - perhaps we would just need to put high-powered cell towers so the individual phones can communicate efficently.
        • As I understand it - if a Cell phone can't get a signal, it boosts it's power output in an attempt to connect.

          My understanding (and it may be wrong) is as follows:

          - The cellphone listens for a carrier signal from one or more towers.
          - If a signal is detected, only then does it attempt to register with the transmitter.

          That way a phone doesn't burn through its entire battery every time you leave a coverage area. There's really no reason to transmit anything if you can't hear the tower (which is a more powerful transmitter than you are.)

    • Maybe they have logs that they can check and extrapolate information from?
    • By now i would guess that most phones would have run out of batteries. However some people may have been smart enough to turn their's off for most of the time, only occassionally calling. If resucers get close, then they could turn it on and start calling.
  • And what about a link to the CNN interview? Or isn't it on the web? J.
    • Hey, sorry for no link, but I saw it on the new over a late breakfast. I didn't have much time, so the best I could find was that FEMA link.
      • np :) If I sounded offening, please excuse me, wasn't intended. But I thought you saw this on the web. (hehe.. i know cnn only from the web. don't have a tv set) Have a nice day, J.
  • http://www.markvd.net/
  • According to news reports earlier in the week, there were indeed quite a few cell phone calls from those people trapped under the rubble. But right now after 4 days, those people would have died due to injuries and lack of water and food. I just wonder, if they have this kind of technology, why didn't they use it earlier?
  • One would hope that those trapped would have realized rescue efforts were going to take several days or more and powered down their cell phones in order to conserve the battery.

    But I suppose that is speculative, at best.
  • Its been a few days already. How are they going to find signals from phones whose batteries are almost dead, through rock and other signal blockers?

    Most peoples' phones work fine for a couple of days, but unless everyone down there has an extra battery pack or a working charger and plug, their cel phones won't do them much good at all.

  • Not just Lucent (Score:2, Informative)

    by CE@UIC ( 14343 )
    The company I work for is doing the same thing. They haven't done it already because it's never been done before. With CDMA phones it's not as simple as looking for a specific frequency, they have to identify the phone by the code it uses to decode the signal.
    People I work with have been working very hard to modify the basestation software to allow them to search for a particular phone. They are basically strapping a small base station to their back and walking around the rubble.
  • It's the usual argument. Which would you rather have - anonymity, or the ability to at least *try* and stop things like the WTC crash from happening?

    I know it seems ridiculous to you Americans, and I'll probably get flamed to oblivion (though that is not the intention.) But if it means even the slightest chance of preventing this kind of thing from happening again, I'd sacrifice some anonymity any day.
    • last time i checked, this technology would NOT make it easier to stop terrorism...

      if it works, it might be easier to track down the phones of the people (if I was told to evacuate, I can't promise that I would grab my phone off my desk)...

      it sounds like the tracking is a great idea, but i'm thinking that it may have already been too late...

      God Bless the fallen and the rescuers...

    • Well, first, it's worth noting that this technology is being used (at least at the moment) to find people-- or sadly, more likely bodies-- lost in a huge pile of rubble. I haven't seen any discussion of the possible use of cell phone location technology to prevent terrorist attacks... one wonders how it would help, actually.


      Second, it's not anonymity that Americans hold dear so much as the freedom to communicate without fear of repercussion. Freedom of speech and of assembly are guaranteed by our Constitution, and most of us believe those guarantees to have been well-considered. Those two freedoms are critical to the notion of a democratic society.


      Finally, your comments (though I think you perhaps misunderstood the application of the technology, in this instance) do not seem ridiculous too all Americans, especially right now. I had a long, sad debate with a friend of mine on the very subject last night.

    • Re:Well... (Score:3, Insightful)

      by ergo98 ( 9391 )

      But if it means even the slightest chance of preventing this kind of thing from happening again, I'd sacrifice some anonymity any day.


      It is incredibly tragic that people are rewriting the bounds of freedoms at a moment of emotional upset (sort of like going grocery shopping when you're hungry): i.e. Western society has done just fine for quite a long time building the best society on the planet, and in a heartbeat people are willing to take it all away because of a single incident (BTW: Seems to me that we could just intrude in that freedom of religion worldwide and suddenly these problems wouldn't exist...you're willing to give that up right?). The reality is that government backdoors in encryption, and tracking for cellphones works to catch one single type of person: Idiots. If I were a criminal I would dream of a cell phone that sent the location (picked up by GPS...triangulation would be tougher but of course with simple relays you could get around that no problem as well. Maybe stick the cell retransmitter on top of a public bus and use it as a relay, ad nauseum) as I'd reverse engineer it to give a location several miles off: Keep the law busy for a while, and as we know law enforcement and intelligence has been FAR too much in love with technology as of late, so you can bet they would sit looking at their screen saying "Damnit he's got to be here! The screen says so! Look again!". It's hilarious that instead of intelligence or physical protective measures (such as secured doors on planes which are so dumbshit obvious that it boggles the mind) people look at the IDIOTIC (I mean mentally deficient. Seriously this gets me in a rage that people and their quest for the illusion of safety can be so god damn stupid) measures such as "Ban MS Flight Simulator!" or "Don't allow Arab men to buy one way tickets!", or "Let carnivore listen to all emails for secret words that'll give away the terrorists!". The illusion of safety, and then everyone can go back to their lives pretending that everything is hunky dory and they're just fine and have nothing to worry about because damnit the government has carnivore, backdoors in encryption that only law abiding people use (oh, also which organized crime uses to get at your information too while you're illusioned into thinking it's secure), and the right to cavity search any random Joe on demand....until the next attack occurs. Then you just have to reduce freedoms more right?

      • Brings to mind the argument I've been having with my wife. On the day of the attack, some FAA spokesman was on the air proclaiming how well trained the terrorist must have been due to the difficulty of flying such a large plane. My immediate response was, "Bullshit, they just want to inflate the enemy so that they don't look so pathetically insecure." Think about it. If anyone could pull this off this means that we don't have a chance in hell of covering our asses.

        Well, guess what. I've been hearing people who actually fly plane saying how easy this would be. Take off and landing would be hard without the proper training and experience, but aiming at a spot and flying the plane into it would be simple.

        The government types want you to think they can protect you completely, and they want you to hand over all your liberties as payment. The fact is they can't protect you from BinLaden or McFey (don't know the correct spelling of his name). If someone wants to blow something up, they WILL find a way, EVEN in a police state.

        If you don't believe that, then explain how Allies guerilla operations can take out Axis infrastructure (even if only a small amount) during WWII when Germany was a POLICE STATE!!

  • Maybe another simple way (Score:1, Interesting)

    by Anonymous Coward
    A working cellphone transmits regularly; how about
    a field meter with a directional antenna?
  • I remember an article on Slashdot quite a long time ago that there was some technology being developed for military use that would detect the electric signals emmitted by a human heart's natural pacemaker. The military application would be to allow soldiers to see targets and members of their own force, even when distinguishing a target using infared or night vision would be difficult.

    Maybe someone has a link to this story? Or more details about the technology? It sounds like it would be useful in a situation like this.
    • I think you read it in "Rainbow 6", dude!
    • Some people did try this once upon a time. As it turns out the electrical signal in a heartbeat is so weak that it gets drowned out in the natural background almost immediately. In fact, IIRC, you'd be better off with a directional mic trying to listen for heartbeats (which isn't very good either).

      One of the companies trying to do this stuff did actually develop a device for something like $50,000 but independant testing showed they were essentially a fraud. Whether the device said there was a heartbeat in a particular direction was purely a function of how the operator was holding and using it, and had no relation to actual heartbeats.

      After that fiasco the whole idea pretty much got thrown out.

  • Details? (Score:2, Interesting)

    by humblecoder ( 472099 )
    Does anybody have any details about exactly what this "technology" is? Does it require the cell phone to be on and powered, or can it find cell phones without a charged battery?

    I also heard on CNN that they can use this "technology" with Palm Pilots as well, but they were very sketchy on the details.

    • All I know is:

      * It is supplied by Lucent
      * It is being called a "Radio Frequency Sniffer"
      * You must dial the device for it to work, so I imagine the device has to be on
      * It would work with anything with cellular capability, like PalmPilots with cellular modems

  • Call Center (Score:3, Interesting)

    by ghasty ( 513881 ) on Saturday September 15, 2001 @07:00PM (#2304220)
    I've actually been at the Wireless Emergency Response call center most of the morning and am scheduled to go back 3am Monday. Yes, it may not be a good chance...but it's still a chance. You can still hear the horror in people's voices. Being in Georgia we've been so removed from the victums and family...being at the call center really brings it home...

  • Last night I dug up this passage from Hitchhiker's Guide to the Galaxy and typed it in:

    The Earth.

    Visions of it swam sickeningly through his nauseated mind. There was no way his imagination could feel the impact of the whole Earth having gone, it was too big. He prodded his feelings by thinking that his parents and his sister had gone. No reaction. He thought of all the people he had been close to. No reaction. Then he thought of a complete stranger he had been standing behind in the queue at the supermarket two days before and felt a sudden stab--the supermarket was gone, everything in it was gone. Nelson's Column had gone! Nelson's Column had gone and there would be no outcry, because there was no one left to make an outcry. From now on Nelson's Column only existed in his mind. England only existed in his mind--his mind, stuck here in this dank smelly steel-lined spaceship. A wave of claustraphobia closed in on him.

    England no longer existed. He'd got that--somehow he'd got it. He tried again. America, he thought, has gone. He couldn't grasp it. He decided to start smaller again. New York was gone. No reaction. He'd never seriously believed it existed anyway. The dollar, he thought, has sunk forever. Slight tremor there. Every Bogart movie has been wiped, he said to himself, and that gave him a nasty knock. McDonald's, he thought. There is no longer any such thing as a McDonald's hamburger.

    He passed out. When he came round a second later he found he was sobbing for his mother.

    Of course, Dent's thoughts were of complete and utter physical destruction of the entire planet. However, the comparison is not totally unjustified since many of us feel that the entire culture of the world has changed in an irreversable way. In a sense, the old Earth is gone.

  • There are multiple ways to locate a cell phone or pager, and I suspect they will use all of them. Some have already mentioned GPS, that's rare to non-existant in today's devices. More likely are triangulation, or simple signal strength.

    Several cell providers have been using triangulation to work towards the E911 requirements. Rather than implement expensive GPS solutions, they simply track a phone from multiple antennas, and triangulate the location of the phone from that. While normal accuracy is only +- a quarter mile, in an instance like this local portable cells could bet set up around the site and generate high accuracy.

    Even if that can't be done, making a cell phone talk to the cell site (telling it to reregister, for instance) would allow you to listen for its signal with a strength meter. Walk away it reduces, walk towards it gets stronger. In a relatively small area like this it would work well.

    Of course, there is also low tech. If they ring the phones, and make the area quiet, they can hear them ring. For those very near the surface this could be particularly effective.

    Others have commented on batteries. Many cell phones are probably running low, but I would venture about 1/3 of today's phones last a week on standby, and would still be able to ring. Two way pagers and other communications devices often last longer, two weeks or more at a go. They could still have a huge number of these devices active. That said, they need to be careful. Ringing them too much will run out batteries.

    I wish them luck, it's a good idea.

  • To clarify on "being used to find survivors" (Score:5, Insightful)

    by SMN ( 33356 ) on Saturday September 15, 2001 @08:17PM (#2304332)
    After seeing this on CNN and reading an article linked to by Drudge, it would appear that the purpose of this isn't what it might appear to be at first. Some quick posters appear to think that it's being used to locate survivors within the rubble. As one poster pointed out, it simply isn't precise enought to pinpoint where in the debris the phone is, and it's particularly inaccurate at finding out how deep the phone is buried (ie, how "high" it is).

    Instead, they're only trying to get a very general location of the phones, to determine whether they're at "Ground Zero" or not. If not, they could potentially be used to find if somebody's at a hospital in a coma, or if they somehow got out of NYC in time and for some reason haven't been able to contact someone.

    These phones aren't really being used to locate the survivors, they're being used to gain some clue as to whether a person is buried, or might have survived. It won't do a great job of locating people, but it will help discriminate if a person is "likely dead" or "might have gotten away."

    I also heard that no actual calls have to be made to trace a phone's location, but I'd guess that it must at least be turned on and able to receive a call. And yes, as many posters have said, batteries are going to be a problem this many days later. But any more information on what happened to these people will surely be welcomed by their families.

    • As one poster pointed out, it simply isn't precise enought to pinpoint where in the debris the phone is, and it's particularly inaccurate at finding out how deep the phone is buried (ie, how "high" it is).

      You can't do this simply because you don't know exactly which bits of rubble are where in a pile of rubble, thus you have unknown attenuation of signal.

      I also heard that no actual calls have to be made to trace a phone's location, but I'd guess that it must at least be turned on and able to receive a call.

      Cell phones periodically attempt to register with a base site whilst they are switched on, regardless of if any calls are being attempted.

  • Noise triangulation... (Score:4, Insightful)

    by zulux ( 112259 ) on Saturday September 15, 2001 @09:07PM (#2304398) Homepage Journal
    If you could get a cell phone to answer a special emergency incomming call, and if you could place a cell tower close to the site - you could do a triangulation of the vicem by setting up three loude noise makers spaced far appart. Each would trigger in sequece, and a triangulation could be made by determining how long the cellphone took to hear the noise. This would allow rescue workers to fin the locations of the phone - even if the GPS signal can't get to the phone, the noise could.
    • The problem is depth. Triangulation typically works because there is only one unique point that is X units away from location A, Y units away from location B, and Z units from location C in two dimensions. I'd guess that you could set up more "noise makers", possibly at different heights, and this might work in theory -- but in practice, I think it's unfortunately too far-fetched.

      • Triangulation works in three dimensions. Two spheres intersect in a circle, three spheres (a circle and a sphere) intersect at two points. One of the two points is generally an impossible answer (too high, for instance). This is how GPS works, with three satellites (although it is more accurate with four).
    • If you could get a cell phone to answer a special emergency incomming call,

      You can. As part of the process of connecting a call the cell towers send a message to the phone, asking it to tell them where it is ("Joe, can you hear me?"). The phone responds with a short transmission ("I'm Joe and I hear you!"), and the cell towers that hear the response can measure the signal quality and decide which one has the best signal path to the phone. Then THAT one places the call. If none have an adequate signal the call isn't placed, so the phone doesn't ring.

      This means your phone can be "pinged" and located without it doing anything to notify you. If you haven't added an external detector (i.e. diode and piezo sounder) to detect the transmission you won't know it's being done.

      I understand that law enforcement agencies already have equipment to do this. Perhaps this is what they're bringing.

      and if you could place a cell tower close to the site

      For "cell tower" read "small box of test equipment with a little antenna at a known point."

      - you could do a triangulation of the vicem by setting up three loude noise makers spaced far appart. Each would trigger in sequece, and a triangulation could be made by determining how long the cellphone took to hear the noise.

      Simpler: Have four (or more) antennas at known relative positions listen for the signal and measure the DIFFERENCE in the arrival time. (You can also measure the PHASE of the signal to determine the "difference in arrival time" to as much less than a cycle of the signal as you equipment can measure the phase.)

      The surface of constant path difference (result of measuring with two antennas) gives you a hyperbolid. Add a third antenna and you get the intersection of two hyperbolids - a curved line. (Don't recall the family of curves at the moment.) Add the fourth and you're down to two points in space.

      You can also do this with four passive devices measuring the time between a cell tower's "ping" and the phone's reply, though the computation is a bit more involved.

      Problem is that this is the behavior in free space. Add anything that bounces the signal about or shields the direct path and you're fouled up. And the phones are under tons of material, much of which reflects microwaves.

      Forget about measuring phase to locate down to inches - you'll have to depend on the arrival time of the start of the signal, before the additional signals that took a different route arrive. Still good for feet or so. But if you're lucky what you'll find is the hole the signal is coming out of - and if you're not you'll get a bogus location in the vicinity of such a hole or perhaps the vicinity of the singal itself, due to signals taking different bank-shots to different antennas.

      Still, I expect it would point you in the right direction and usually send you to the right room-sized volume. And as you dig out more obscuring stuff the quality of the location would progressively improve. That's good - as you get closer you need a better idea where you're goiong, to keep from crushing the person you're after.

      Also: There's no reason why you couldn't bring test equipment that, once it got a good path to the phone could CALL it, so (if the person was alive and awake) you could talk to them. (Though it might be good to use the call mostly to tell them to stay off the phone but leave it turned on, to conserve the battery.)

      Which brings up one last downside: Some people may have either used up their batteries trying to call out while there was no working base station in reacy, or turned off the phone to conserve power for later.
      • - you could do a triangulation of the vicem by setting up three loude noise makers spaced far appart. Each would trigger in sequece, and a triangulation could be made by determining how long the cellphone took to hear the noise.

        Simpler: Have four (or more) antennas at known relative positions listen for the signal and measure the DIFFERENCE in the arrival time.

        I wasn't quite clear. One of the antennas sends the interrogation, all four listen for the reply and measure the arrival time.

        Ideally they measure it relative to the arrival of the reply at the other antennas, not to the interrogating signal, so the time it takes the phone to figure out it needs to send a reply doesn't make clocing inaccuracies in the receivers degrade the accuracy of the measurement.
  • This is an incredible story [newsoftheworld.co.uk] about some of the amazing new military technology we've got.

    We'll need it, too, if this guy [ornery.org] is right. It's a well-written essay.
  • ...who reflexively twitched at the naming of FEMA?

    Too much Deus Ex, I guess...

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