Recently, four of the six battery-operated smoke alarms in our house have started going off every few days, for no obvious reason. The four that have been going off are of three different models, including both ionization and optical types. They are not wired together. We have a CO alarm which has not been going off.
This happens in the absence of any obvious source of smoke, dust, water vapour etc.
So the question is: what, apart from the obvious, would cause multiple types of alarms to go off?