On Sat, 27 Aug 2005 19:39:32 GMT, Hogger said in
rec.radio.scanner:

As far as specifically tracking someone RECEIVING radio frequencies,
I'm not familiar with any piece of equipment capable of doing that.

If such a device existed, I have no idea how it would differentiate
someone's AM/FM stereo, wireless router, baby monitor, coordless
phone,or garage door opener from a scanner. (Yes, I know, some of
them transmit.. and that can be detected.. I mean from the "receiving"
point of view, for example.)

By the frequency of the local oscillator, but that's very iffy as
legal evidence.