During recent household decorating shenanigans we lost our Smoke Alarm. So I bought a replacement, what with not wanting to wake up dead one night. The new smoke alarm is probably very good at detecting fire. It's definitely very good at detecting steam. It went nuts after I'd had my shower, much to my annoyance. It's in exactly the same spot as its predecessor, which was no problem at all.
A quick search of the Amazon reviews found that yes, this model is known for steam powered false alarms. Incidentally, the reviews for smoke alarms were an interesting read. There were lots of reviews mentioning how small and neat the alarms were, how quickly they were delivered, but hardly any along the lines of "If it hadn't gone off that night when the bread maker started to smoulder we'd all have died in our beds...."
However, the good news is that a proper search of the area turned up the original (and a lot newer looking than I remember) alarm which has been fitted with batteries and is now working a treat. At least I think it is.