Americium in smoke detectors is safe.<quoted text>
And in layman's terms, we call this "safe."
It's a beta particle emitter (I think)-- that's just energetic electrons.
You can easily stop these with some metal.
So the slug of americium is housed in an aluminum box, with carefully slotted holes-in. They are double-slotted, such that there is no direct line from the slug to the outside. Smoke will follow the twisty passages, becoming ionized by the radiation inside.
Okay, so **some** radiation gets out-- sufficient to trigger sensitive Geiger counters.
But less radiation than a few minutes under the sun.
It's all in the intensity, and length of exposure.
But I would not recommend **eating** a smoke detector...