When the FBI Guys Come Knocking...

[Nomen Nescio]

  Tim's idea of a closed circuit TV is the best approach, and something I've 
been thinking of for a long time. By far the best way to interact with anyone 
you didn't want around. You'd want to couple it with a computerized voice 
interface that made it sound, at least, that they were dealing with a machine. 
"State your full name"
"Face the camera"
"Turn face left"
"Turn face right"
"Hold ID up to camera"
"State business"

 and at some point a speaker off to the side or behind them could emit the 
distinct sound of a 12ga pump action being being worked, followed by a:
"Leave property now"