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?