he probably wanted you to sweep his car for cop bugs!

this is very easy to do. actually tracking/proving hf transmitters are there is very easy. you can do it with a dynamic microphone and a micamp. its a very sensitive system (usually above 60dB) and even the most faint electomagnetic devices will sound like f-ing beacons when you plug in headphones to listen. basically all electronic stuff makes a signature. and if you find a signature/sound/disturbance where there should be none then you know there is something weird going on.

I can record my shielded computer psu electronic airborne noise from about 0,5m with full amplitude.

Most if not everything will show up way above 20khz. though. and as we all know humans can only hear up to 20khz. but the devicec will either am or fm or pulse modulate at way lower freq than this. so its very audible.

The reason i know this is that i heard a quite loud HF/noise sound when playing music at full blast in my stereo.

And i simply investigated. built an antenna. hooked sh1t up. and listened to all my all my electronics. In my case the stationary computer psu was the offending part. and you could see it far far away on the spectrum analyzer in my daw!!

i once read a book about electronics. once.