I bought a 2 pack of these alarms and they did not work. Very slow to detect smoke on one and the other simply did not even go off. I swear I almost burned my house down trying to get these stupid alarms to go off. Errr...
Luckily Amazon's incredible customer service gave me a refund despite being over the 30 day return policy (I had bought them for an apartment I was renovating and opened them when the reno's were finally done - which was more then a month after I bought them!)...
So even though the alarm's did not work, I got a full refund thanks to Amazon's awesome customer service so no harm done : )