I suspect poltergeists.
It's a communist plot!
On a side note, the radioactive elements in old smoke detectors make great random number generators.
Humidity plays a very important role in the triggering of false alarms.
If water vapors enter the detection chamber, they will refract the IR light and cause the photodiode to trigger an alarm.
It is best to keep the smoke detectors away from sources of heat or cold.
Pay attention to dust also, as it will have the exact same effect.
Insects cause a great deal of false triggering. OT Cockroaches also eat foam surrounds!