(not a lawyer, if one shows up, listen to them) Generally speaking, you can listen to anything, as long as it's not for commercial gain.
The exception to this is mobile phones, because it was trivial to listen to them using children's toy radios.
There's apparently some uncertainty around handling of encrypted emergency services communications: https://www.rtdna.org/content/scanners
https://www.fcc.gov/consumers/guides/interception-and-divulg...