Where were your faulty detectors? My ex-girlfriend's dad used to do testing for a smoke alarm company a while ago. I learned an interesting thing from that. You know what they use to simulate smoke when they test smoke detectors? Hair spray. The fine mist is actually pretty good at tricking the sensor into thinking there are smoke particulates in the air. This also leads to an interesting failure scenario for many home smoke alarms: those close to bathrooms or in women's bedrooms tend to get gunked up with hairspray.