yep, you are right. Smoke detectors do contain a little nuke, as do your average motion sensors gadgets, like those outside house lights that turn on whenever something crosses "the beam".
For a real treat, you might wanna purchase an inexpensive Zap Checker and or Geiger Counter, then walk around your house and neighbhorhood finding the hot spots. The former is basically an RF meter that can be dialed into ranges of sensitivity across a spectrum of frequencies. I've seen some advertised around $100. That might seem an expensive toy to some, but a most useful tool in the hands of the right others.