Smoke detectors rely on a circuit powered by atomic fission ionizing the air. It isn't their power source (they still need batteries), but it is a safe way to get continuous electricity.
There's probably a way to get a little more power out of it without being too dangerous. But then we'd have ordinary citizens buying things over-the-counter that could be abused in bulk. And I don't see any hassle being worth an extra free outlet or not replacing batteries.
https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/s...
There's probably a way to get a little more power out of it without being too dangerous. But then we'd have ordinary citizens buying things over-the-counter that could be abused in bulk. And I don't see any hassle being worth an extra free outlet or not replacing batteries.