Cdex, Inc. (fka CDEX)

[Crow3]

Lots of ways to simulate a desired response. In the ELF days he pointed it a bucket of sand and got a red light if benign, a green light if there were explosives within.

Such easily arranged indications got more sophisticated later. But still the same principle.

If the demonstrator has a kind voice, warm and friendly, a wee sense of humor, a grandfatherly look, white hair and such, so much the better.