Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Many defective units

We have 9 of these in our house and have had to replace almost all of them in the seven years we've been here, some of them more than once. These are supposed to be top of the line smoke detectors but I don't know why. They break easily and don't seem worth the extra money. Now when they go off, we assume its not a fire since they have gone off so often because they are broken - what kind of lesson is that. If they ever do detect a real fire, I hope we don't assume they are broken! It's also hard to find replacements for them. Don't buy these!