Fog machines

 I agree with David & Don, sorry Jake!

Any airborne particles obscuration entering the detection chamber, will disrupt the sensor & cause an alarm state to be triggered. Wether this is with an Ionization, Photoelectric, beam or air aspirator type detector.

The alarm situation can also be caused by a dusty enviroment, which can be prevelent in theatre.

Fog of course normally hugs the deck to find the lowest piont, while smoke rises & this is the normal cause of an most alarms. Because the detectors are usually placed in the highest pionts of a venue.

In a lot of situations where smoke is prevelent for any cooking, such as in the 'Toast Effect', the 'smokey' can be easily changed out for a heat detector or even a 'toast proof' one.

The Australian Opera used to endorse a paticular brand of liquild for smoke machines years ago, but I think  this was more of a commercial gimmick sonsorship for the AOC & mind over matter to reninsure the worbling luvvies. It still a heated liquid & causes smoke.