From my rather rusty knowledge of radio, most radio receivers use a superhet 
circuit, so that the incoming signal is mixed with a local oscillator, giving 
a fixed intermediate frequency (IF) that is more easily amplified. The
detector detectors work by picking up IF re-radiated from your radar 
detector. In Britain, where one has/used to pay for a TV licence, there 
are/were TV detector vans prowling the streets, looking for people who hadn't 
paid their licence fee. They had a couple of long solenoid antennae on the
roof, and I believe could triangulate an operating TV from the IF. 

I wonder how much of the IF is radiated back from the detector antenna, and 
how much from the rest of the module. It might be worth putting the detector 
in a proper RF shielded enclosure.
