at least in Europe the Communications Ministries (Ofcom, Agentschap Telecom, BNetzA, ARCEP etc) actually make it clear that any device which sends radio signals into the airwaves can be monitored by all sorts of people you might not have wanted to do so [including cops and govt security organisations]; it can be geolocated (mobile phones wouldn’t work otherwise) and if the cops ask the Communications Ministry officers to assist with a criminal investigation they will do so provided it is in line with a Court judgment or domestic legislation.
They even tell you where all the “spy centres” are nowadays. Our main one for the UK is at Baldock in Hertfordshire; although what they usually do is just check what radio signals are present and that everyone is playing fair and using correct frequencies/TX power/modulation type and not accidentally or deliberately causing harmful interference.
There are various antennas and other monitoring equipment on every roof in big towns and cities but 90% of the time they are not bothered with the actual content of the signals but are connected to test equipment used for keeping the airwaves clear for important stuff like public safety transmissions.
if you go to the BNetzA site there is a link to a map of Germany where all the larger monitoring stations are shown on there and you can even look at the anonymised data for each frequency band yourself.
Recently the Ofcom man actually sent me a license which actually permits me to transmit encrypted data on certain radio frequencies (I didn’t think it was allowed!); although I had to tell them where I would be doing it; any messages I send have for legal purposes and it is unlikely to be anything that GCHQ can’t easily decrypt (plus any decent scheme halves the range and uses up more battery power on portable equipment).
It also permits me to hire various specialised items of comms equipment to others; but I am still responsible for how it is used so its most likely to be operating in clear transmission mode anyway – its limited range and specialised nature means its not that trivial to monitor and the information of limited use to those who are not the intended recipients.
