Fire Alarm

Hey all,

We moved into a new house about 3 years ago and have been plagued by nuisance alarms ever since. They happen most often in the middle of the night, but aren't uncommon in the daytime.

I have:

• Replaced all the old hardwired detectors with new battery-only ones thinking it might be caused by EMI.
• Ruled out insects crawling into the detectors.
• Sealed the electrical boxes thinking it might be dust from the attic.
• Installed an excellent filter system in the HVAC.

Other random info:

• Only the ones on the second floor go off. There are five upstairs and two downstairs.
• I'm pretty sure one (and only one) of the false alarms was caused by humidity from a shower.
• Seems like they're happening less often since I installed a new HVAC system, but that could be due to less dust or due to smaller temperature swings (less of a setback at night).

I think at this point I want to get some fancy multi-criteria alarms, ones that are specifically for reducing your nuisance alarm rate. Also for increased capability, though - one of my coworkers just narrowly escaped a housefire with his wife and dog. Their fire alarms failed to go off and he was only woken by the sound of the flames.

Any suggestions for multi-criteria alarms that work with hardwired 120VAC three-pin connections?