Americium and Californium are currently used as alpha sources in smoke detectors. The NRC has waived Byproduct licenses for these little uses, but usually, anything from a reactor is regulated. This sounds like a "burner" application, where something with a short halflife and a high specific activity is used as a heat source. Strontium 90 was used in a space power application for the early SNAP satellite battery.
But I think that there are enough objections to this scheme that we will probably never see it in use.
One thing to remember is that the Cassimi(sp?) satellite was sent up a couple of years ago with 73lbs. of plutonium on it. The same rocket might have been propelled with only .73lbs. of Am242m. I'd still like to tie it in with nuclear waste disposal to make more of a market for it. I mean, who can argue with cleaning up nuclear waste?
Californium in smoke detectors? Gawd, I hope not. 252-Cf is one helluva neutron source. You don't want neuts in a smoke detector. Besides that, its tough to make (you're talking about something like a 14n-capture reaction in uranium, and thus is bloody expensive. Last I heard, ORNL was selling it for something like $50 per microgram. And since the neutron emission rate is about 2.8 million n/sec for a microgram, I don't think we want that in smoke detectors. Americium is the material of choice in that application, I think.