Like say audioguru
An RF probe was used a hundred years ago when there were hardly any transmitters.
Today it will pickup every radio station, TV station and taxi-cab radio in town.
Millions of other radio transmitters are also used and will also be picked up.
UNLESS YOU ARE ON MARS or in a 3rd world country.
I can add any local oscillator in receivers , synchrony oscillators from TV set and CRT monitors.(It is hard to write all interference source today)
It is correct in any city. Simple RF probe cannot help(only make wrong image).
PC have also RF and will be cause a wrong measurement(I was use industrial receiver and wonder "how many signals are in specific amateur radio frequency?" But all this signals was from local area network in building 141MHz 144MHz etc.From common PC)
But it is not impossible mission.
Look like joke how simple device can easy work for this task.(Proven by government agency long ago)
Because most bugs are triggered through certain frequencies, it is very simple “to build a small sweeping device that will trigger any bug present".
Or even only passive RF receiver.Bug will be triggers with own signal.
Add just , remove coil from original draw. Instead make a resonator on 150 MHz so call Lecher resonator
http://lea.hamradio.si/~s53mv/counter/lecher.jpg
But for this project must be shorter than 1/4 wave length(300/150=2 meter/1/4=50 cm so must be shorter much more) and to tune up, use variable capacitor.This cannot give you narrow band but it will be cut off much more interference. Also leave meter to see signal strength but not importance. Importance is add audio amplifier to run speaker.
Why, bugs are to simple transmitters low power, so if you build simple RF wide frequency receiver , passive receiver. And
importance
do not use headphone etc for signal presence no. Use speaker only, and what happened? Bug pick up audio and transmit , when a simple device receive RF signal you can hear on speaker and when you near bug(few feet)
bug will be pickup signal from speaker then amplified and transmit, bug detector receive RF from bug this will be appear like sound oscillations.(Like whistle sound) And you do not need to know exact frequency of bug and forget other source of RF, they cannot create negative feedback to make sound oscillations.
Phone bug use electricity from phone line and work only when pick up phone(easy close the electric circuit and bug in serial with phone start transmit RF). So pick up phone receiver place near phone (live open line to bug transmit)
I believe this is electronic project easy to do.(Also standard anti surveillance procedure) Good enough? For simple device?
How to do it for hidden camera I do not know(can help only what I was try), and such this device are integrated mostly camera and low power transmitter on pretty high frequency. But still are rule
no transmitter can be hidden. Even transmitters in burst mode radiate RF , and bugs device are pretty simple and radiate RF all time.(Audio or video same thing).