> have 3 or more microphones, piezo's, or other vibration sensors
> connected to it. Monitor received analog signals with a fast micro

The US military have a microphone system called Boomerang for
triangulating snipers. I saw it on 60 Minutes not so long ago

http://www.gizmag.com/go/4497/

http://www.youtube.com/watch?v=dYgsGoAlb1s

I don't know if it's precise enough for targets though. Two IR
curtains (one vertical, one horizontal) may be better

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