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Science Technology

Scanning For People Through Walls 19

cloudmaster writes: "RADAR-based "flashlight" for detecting movement (and respiration?) through walls and clothing: There's a bargraph that rises and falls as a person on the other side breaths... It needs to be held perfectly still, or it will detect it's own movement too, though. I wanna know why they don't just use an acelerometer to detect the devices motion and subtract that from the detected motion?"
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Scanning For People Through Walls

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  • I've been keeping my eye on Ultra WideBand for a while now; it has very surprising uses in positioning, communication and measurement. There's even a working group [] which tries to keep tabs on the entire area.

    Years ago I heard about time-domain []. I don't work for them but when I first heard of them I thought it was vaporware. I'm kind of sorry I didn't take them seriously the first time around.

  • by Anonymous Coward
    Michael, I sense three people inside the warehouse.

    Thanks, buddy. How about a little Turboboost?
  • by cperciva ( 102828 ) on Tuesday April 17, 2001 @08:22PM (#284103) Homepage
    I wanna know why they don't just use an acelerometer to detect the devices motion and subtract that from the detected motion?"

    I'd guess that they don't have accelerometers accurate enough for the purpose. They're dealing with *very* small movements.
  • In the article it states that 8 Inches is the most they can do, question that arises in my mind which I missed in the article is how about going through a 4 inch wall then say 2 meters and then a 3 inch wall will it still detect motion ? From my understanding the use would be for for instance police officers, I do not know but I would at least assume that there is such a thing as hallways. Three meters is not that much, if you plan on ambushing some police officer now you just make sure you are three meters away which in most house is possible you take your semi automatic and as soon as your hear the door being busted down, the falsy lured into safety officers will have their vests loaded with bullets
    -= Free your mind and your Ass will follow,
  • i think an accelerometer would be too easy. they need a second device that uses precise lasers to detect the motion of the first machine. then they need to put very precise accelerometers on the laser so as to ensure it isn't moving either. then they need to ask everyone on the other side of the wall to wear accelerometers, that way they can ensure they are not moving.
  • Not true at all. I've used normal accelerometers that are very sensitive. Indeed while I was holding it "still" and reading the data realtime, there was quite a bit of movement recorded. I think the only reason why they don't use it is that it's expensive.
  • Or just stick it on a tripod...
  • i was merely trying to be humorous. unfortunately, my comment does not read that way. i understand that accelerometors can be very sensitive. just want to add that i have taken vibrations classes where we used very sensitive accelerometers that cost around $30. this does not seem(imho) to be a lot to pay for a piece of equipement that can see through walls. but maybe $30 is a lot in comparison to the rest of the equipement used for the wall radar.
  • That reminds me of farsights in perfect dark.
  • I feel bad for the dog that accidently gets shot when the sensor reads its motion and the police are expecting to apprehend a criminal inside the house.
  • Not only would you have to have a very sensitive (ie expensive--- they DO exist, tho) accelerometer, but you'd have to deal with the fact that accelerometers only measure... errr... acceleration. If an object is moving at a speed of 10 inches/sec and it is activated (along with its accelerometer) then the accelerometer is going to have no clue about that 10in/sec speed. It'll only register something if that speed CHANGES. Hence the name...

    We should be letting robots with infrared, electromagnetic, and audio sensors do all this, anyway.
  • but maybe $30 is a lot in comparison to the rest of the equipement used for the wall radar

    The article indicates that the target sale price for this RADAR unit will be $1000-$1500 per device. With the accelerometer you mentioned, I guess they will have to bump that price to $1030-$1530. :)

  • by human bean ( 222811 ) on Wednesday April 18, 2001 @09:21AM (#284113)
    we had all better stock up on aluminum foil before the drug dealers and terrorists start buying it up for use as wallpaper. :)

    Or maybe the mylar metallic print wallpaper from the seventies will make a return. :(

    Since it detects motion, one wonders how well it does with differentiation, what happens with large dogs, kinetic sculpture, mobiles, etc.

  • IANAE (engineer), but I've heard of other applications where accelerometers were used to keep track of position. I would guess that they just need to (numerically) integrate a couple times to get the velocity and position vectors successively.

  • by Anonymous Coward
    There's movement all over the place!
  • The article was unclear, but it looks to me like it can see 3 feet beyond a 4-inch-thick wall. How much of that 4 inches has to be empty space is not obvious.

    If you know the local cops are using these things, you could play nasty tricks on them. Put a corner cube (or even a little dipole) on an oscillating base at about 6 RPM; there's your "breathing" signature. Give it a little sub-shake at about 70-80 RPM; there's your "heartbeat" signature. Stick a few of these around the house and then hide behind a door in a closet with foil-face insulation in all the walls and Alcoa's finest beneath the cedar on the inside surface. SURPRISE!
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  • Just use foil-faced radiant barrier insulation in the walls and metallic screen in all the windows. If you are blowing insulation, put lots of chopped-up aluminum foil in it (chaff). That will make your house proof against this kind of spy gear, and probably bollux up millimeter-wave radar as well.

    The big question is, do you want to? If the firefighters are using these things to locate people trapped in burning houses, you'd be making a tradeoff between safety in a police invasion scenario versus safety in a fire scenario. I'd be inclined to treat the police as the bigger threat (by the time the firefighters arrive, anyone who isn't already out of the house is probably dead of smoke inhalation already) but you might not want to. From what I can tell, the same areas where cops do a lot of raids are also the areas where fires kill people frequently (and are also the areas least likely to have people taking radar into account when making home improvements).
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  • I saw a similar device about 6+ years go, it was like a normal flashlight, but had an IR mode thing. The flashlight would virbate (quietly) if you pointed it at a human (or something of that IR sig.).

    I'd guess that the IR version doesn't see through walls quite as well as the RADAR version.

    I can't remember what happened in the company, I think they found a nitch in the sex shop industry and changed there business model... ;-)

  • Maybe some of us never read our high school physics books...acceleration is a change in speed, or direction. Any speed, up or down, and any direction.

The earth is like a tiny grain of sand, only much, much heavier.