Licensed US amateur operator here. In general the FCC regulations allow you to listen on whatever frequencies you like, EXCEPT the cellular frequencies (This dates back to the analog era, before cellular traffic was encrypted).
Some jurisdictions may also have restrictions on, for example, using a police scanner in a vehicle, that would restrict listening (even though most of that traffic is now also encrypted).
replyDon't quote me on this, but I believe there's some more nuance to the cellular band issue. What's restricted, AFAIK, isn't simply receiving traffic on those frequencies in and of itself, but:
reply1. Decrypting those communications if they are encrypted
and
2. Selling equipment designed to receive on those bands.
Of course there's not much purpose in sitting around listening to the digital chirping noises of encrypted traffic, but as I understand it, if that's your hobby, that part is actually legal.
(Also a licensed US ham, not not an expert in anything in particular and definitely not a lawyer)
I would be surprised if it were illegal to tune into something being broadcast in public over the air. Decryption is a different story.
replyGet ready to be surprised, because the 800Mhz band used for AMPS (1G / analog cellular) was explicitly carved off as a no-receive zone by Congress because AT&T was pissed[0] anyone could just listen in on any cellphone conversation. I'm told the law actually makes it really difficult to legally sell fully open software-defined radios (SDR), even though nobody uses analog cellular anymore, because you still have to design the SDR to be tamper-proof against attempts to receive 800Mhz.
reply[0] Wikipedia also mentions the existence of cloning tools that would let you copy any AMPS subscriber ID and program another phone with the same number, stealing the subscriber's account. I suspect AT&T was more angry about that.
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