We played with them, but the more affordable ones require a large temperature differential to work well [a human against a 50* F background or a 98* F human against a 1200* F house fire.
In the summers here, it isn't quite as effective as one would hope for.
Dear God, this is one of the dumbest ideas I've ever heard. It's got to rank right up there with CALEA. -Pepper45
Bastard! - TBO