One for each house in a 8 foot square. plug it in. 20 years later get a new one.
They actually exist!!!
In my rock climbing days, I climbed with a guy that did government work in the mountains overlooking China.
Placing sensors, transmitter, and a power supply.
The Sherpa's loved the power supply because it stayed warm, and slept with it!
A minor downside, I believe this device used plutonium, not good?
Might need one or two for each circuit in your house.