Turns out.... you're really supposed to have a few of these - especially near the bedrooms in the house. I was more aware of the need for smoke detectors and... even had myself convinced that only people with gas furnaces really have to worry. Then, a few months ago, a little after 3am, my neighbor (our twin houses share a wall) came knocking to alert me. His carbon monoxide detectors were going crazy and when he got downstairs there was also crazy awful odor and fumes. The detectors really were the "first alert". It was less than 30' F out - so windows were shut tight! When I opened my basement door I smelled fumes too - which I realize is not a characteristic of carbon monoxide - but... his detectors were indicating we had both the odorless killer and fumes. Windows were flung open and the heating folks worked with the fire dept to clear our houses with giant fans. The problem started with a clogged chimney for the furnace on his side. The firemen were adamant that I needed carbon monoxide detectors (and that everyone else does too) and they showed me a spot in the hall near the bedrooms where they recommended I put it. One fireman who lives nearby even offered to put it up later that day when I got back from the store. I'm a believer!

Please read and take note ... look at the manufacture date on them when you get it. I should of read the reviews in detail. Bought a 3 pack, one of them started beeping (5 chirps-end of life) 1 month after installing it, and also after return period. I looked at the manufacture date and it is from Nov 2010. I will throw them all out, nothing worse than this happening in middle of the night. So PLEASE check them before your return period ends.

David

Can't find any CO detector in CA that need battery replacement on annual basis. All CO detectors sold in CA have the 10-year long term battery inside, and they are more expansive than those units sold in Amazon requiring battery replacement.

I have some rental units, I prefer installing CO and smog detectors requiring battery replacement. Mainly, I then have a very good excuse for visiting each property at least on annual basis to replace batteries but also conducting property inspection at the same time.

This CO offered by Amazon is very economical. Can't tell it works or not, as I haven't heard that it ever gets triggered by itself (not due to testing). And no tenant ever reports such incident also.

Installed as soon as they arrived to replace older models that the batteries had expired in (7 year batteries and no maintenance or replacement option). These do have batteries that have to be or can be replaced. The 2nd night after installation, the detector I had mounted in my bedroom (installed all 6 throughout my house) went off around 2:00 AM and awakened me. I immediately shut my gas furnace down and called a HVAC company. They found a crack in my heat exchanger as well as issue with the flue or exhaust pipe that was allowing CO to enter my home. Had I not replaced my CO detectors when I did, I wouldn't be writing this review now. Well worth my investment!! Easy installation and had all 6 up and operating in less than 30 minutes as well as reasonably priced. Purchased this pack of 6 for less that the other 2 I had bought 7 years ago.

The button broke off and fell inside the unit the first time it was pushed. It was only pushed, not hulk smashed or anything.