I saw a wifi camera that replaces a lightbulb. It takes power from the light socket. I don't see why you couldn't make one that also used the power line as a network cable, too. Would require no installation and could be used at your next house.
They are controversial with other radio users, because while the devices themselves don't emit much RF energy, your home wiring and wiring in the street will typically radiate most of the high frequency data into the air, disrupting FM radio and lots of other sub 500 Mhz radio users.
> I was trying to get a good signal upstairs, downstairs, and outside at the same time. I didn't want to run an Ethernet cable out a window or drill a hole in a wall or floor, so I was stuck with moving around a Wi-Fi access point. That was until I realized that I already had wire in the walls—coax cable! But wait, you can't use coax cable for Ethernet communication, can you? The answer turned out to be yes, you can!
Powerline tends to be sorta unreliable and only runs at like 5-15% of the rated max speed, but if you had buffering at the camera to ensure all frames made it to the otherside, you could work around that.