Comment by petercooper
16 hours ago
I was exposed to some of this as a teenager due to a (now dead) family member being heavily into telecoms. You could receive and process POCSAG (the protocol used by paging systems) to pretty much read the entire stream of unencrypted, plain text pager messages going out over the wire. You could also reprogram a generic pager to receive pages for whatever number you liked. You could also transmit your own POCSAG and send any number a page (only within your transmission range).
SMS was also a bit like this in its early days and you could read them coming off the local cell (also true of calls at a certain time, but I didn't see much of this).
I just did a quick search and apparently many pagers in the UK are still running cleartext POCSAG! https://www.reddit.com/r/RTLSDR/comments/1asnchu/are_uk_page...
Yeah POCSAG is not encrypted here in the UK. You can still see all the emergency information from around the country unencrypted in realtime. They even broadcast the details of the emergency and a lot of times it's not nice. You do/did get some bird watching sightings though!
This is still the case today in the US, plenty of pager systems run POCSAG or near equivalents. There is no conditional access or encryption of any kind. Receiving such signals is notionally criminal, but I'm unaware of any prosecutions for such a thing.