Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Great for Safety -- Warns When too Old

I have three of these in my house, and am very happy with them. All CO detectors have a limited life, but these tell you when their life is expired, like a smoke detector beeping when the battery is low.Another reviewer complains about his beeping every five minutes, but the manual explains this is the signal that its useful life is expired (about five years). While waiting for a replacement, as I am doing now for one of my detectors, you can silence the alarm for about 36 hours at a time, by pressing the test button until it beeps.