Traditionally they sent a technician out to read each meter and turn off the electricity if necessary, but there are newer "smart meters" that communicate your usage to the power company (although I'm not sure if those can also be remotely triggered to turn off your power, I would suspect not).
Where I grew up in a small town in the Midwestern US in the 1990s, the meters were usually installed on an external wall at the back of the house. My part of town had underground power lines (good during thunderstorms, bad during road/building construction) and I suspect the meter was right where the buried cable came into the house. Every month a uniformed person from the power company would walk through everyone's backyards taking the reading from each meter.
Fun fact: most utilities and similar services have historically worked this way. I think the cable television company would just send someone to the cable box on the back of your house and flip switches to enable the channels you were paying for. There was always some kid who claimed to get HBO for free because his older cousin worked for the cable company.
Now that I think about it, I recently got a car that's new enough to have Sirius XM satellite radio built in, and I've been wondering how their access control works. Surely the satellite doesn't beam down everyone's subscription status and make their receiver hardware respect that, right? Is my car using the built-in cell phone to check whether I'm subscribed to the satellite radio? Either way, where are the bootlegged satellite radio receivers?
- The stream channels themselves are encrypted or scrambled in a way that is hard to unwind unless you have the keys (keeping non-SiriusXM radios from working)
- Each radio has two important pieces of information: a decryption key from SiriusXM and a UUID (I'd guess 64bit, as that's a pretty standard size for hardware-baked-in UUIDs. It might be 128bit instead). You can look up the UUID for your radio. Both of those things, by the way, are bog-standard now in consumer embedded systems exactly because they help prevent bootlegging.
- Channel 0 is an ID channel that constantly streams out a list of valid UUIDs and other configuration data. An un-activated radio can only tune that channel. When it sees its own ID, it enables the rest of the channels.
Quick sanity check: Assuming they have 40 million subscribers and can pass UUIDs at roughly audio rate (to make the math easy, 16-bit, 50kHz), that makes it about an hour to sync all the users. That can probably be watched by your radio in the background, so it's only an issue for initial activation.
Satellite bandwidth is expensive... Activation time is annoying for customers... The above scheme saves either (or both).
