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on January 19, 2016
I would have given this good reviews, because it is easy to use and I think would probably work correctly, but after having it only a couple of months one unit already started beeping with the ERR code. That code means end of life. The units say they have a 7 year life after start of use. Well, 2 months is far from 7 years, but I checked the manufacture date and it was made in October of 2006, so Amazon is selling 10 year old detectors. and apparently manufacture date does matter, not just start of use.
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on August 7, 2017
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.

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on February 9, 2017
I got two of these to replace detectors in my home and I wall-mounted them (optional). I got these because I'm a ham radio operator and my old downstairs detector (Kidde Nighthawk) kept going off whenever I transmitted on the 40 meter band. After doing some online research I learned that this model is not susceptible to this. It turned out I needed to replace my old detector anyway since it was made in 2000 and they are only good for 10 years! (I also have read that Kidde did not improve their design to prevent false alarms from radio signals until 2004.) It is battery operated only-no AC power connection.

Anyway, these are compact and easy to install. Note: there is not a separate template for drilling the wall mount holes-it is printed at the bottom of the instruction sheet. My only beef with these new ones is that one of them was missing the mounting hardware in the package, so I had to get screws and anchors for that one on my own.

There is a small switch on the back to turn the unit on and there is a separate one-time use switch for deactivating the unit once it's service life is up. It also has a blue backlight to view the display in the dark, and it routinely displays the room temperature on the screen. One button on the top of the unit is used for turning on the backlight; if you press and hold, it sounds the alarm to test the unit.
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on August 28, 2017
Bought this on 30March 2017, and just before the end of August it died. It began chirping like its battery needed replaced, so we put a fresh coppertop in it. It still was chirping. We stepped outside, to verify that it wasn't alerting us to CO levels. Battery out, battery in, another fresh battery, a third new battery - nothing made any difference. We finally just removed the battery.

Apparently, it's the End Of Life death knell for its 7-year life expectancy. Mine has a mfr date of "2016 Jun 07" stamped in it.
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on July 30, 2016
There are two units you can order from this ad. his review is for the CO710. I like the 10 year battery life and it is backed by the warranty. I do wish there was an option to dispaly the current CO reading without having to touch the unit. You can only obtain the peak CO reading when you press the test button.
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on August 25, 2013
The CO alarm pictured is the version with the battery door on the front. It requires 2 AA batteries and once it is mounted, you don't have to remove the unit to replace the batteries. I consider that very convenient! However, when you order this item Amazon is also shipping the unit with the battery door on the back. It requires a 9 volt battery and must be removed from the wall to replace the battery! Both packages have the model number CO400 and Amazon has both styles stocked together. So, if you order expecting the one with the battery door on front, as pictured, you may receive the one with the battery door on the back! I ordered five of them and only one was the one pictured, battery door on front with 2 AA batteries! I hope Amazon sorts out the problem! They did try to get me the correct units and I really appreciate their efforts! But I feel First Alert is really at fault here, because the units are different, yet the model number is the same on both packages!
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Nice little detector. I have mine on a shelf. Since, I have not had a CO leak, thank god, then I can't say much about how good it is as a detector.
But, it is a one time use unit. Once the battery dies, the detector is also dead. That is a good thing!
In my older detectors, the 9 volt that powers them in a power failure, needs to be replaced every year or two. That process in older style First Alerts is annoying as the battery door is awful and the alarm sounds when you unplug it. Dangerous for your hearing!
I think this is the way to go. One battery. Lasts the life of the alarm. Replace whole unit when it shows battery is low.
With these toss when done units, manufactures should also include or let you get, a free shipping label to send it back for proper recycling. Also, maybe offer a slide out unit. Keep the old case, they will send you new sensor guts you slide back in for a cheap price.
The next step is to make these for the same price but make them smart home/HomeKit ready. Alarm app on your iPhone/device alerts you when it detects CO if you are home or not. When battery is near dead, sends an alert. Could be good. I have those alerts NOW with my EVE system for temp, movement, air quality.
I would also like to see a combo CO and natural gas alarm in one unit.
I like separate smoke/fire alarms from CO as that creates a natural redundancy to all alarms should just one battery die, it only hurts one type of detector.
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on December 30, 2017
What I like: It doesn't have to be plugged in, runs on a battery that they say will last 10 years. We'll see. I can set it on a shelf instead of mounting it to a wall. If there is a dangerous level of CO it will display. I hope.

What I don't like: It will only display CO level if it is above some mystery level. If the level is low, or zero, it won't display that. If you try to display the CO level, and it is low, the device goes into test mode. Very annoying!! I don't need a room temperature display, I would rather see the actual CO level, even if it is zero.
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on September 20, 2017
Saved me and my 4 kids lives! I bought this as a backup for my expensive 200 dollar one that connected to my home alarm system. I bought it because I was going to put it upstairs by the heater. Well it went off in the middle of the night and we left the house and called the police. They showed up and tested us, we had to be given oxygen from hospital! Myself and the baby (1 year) had the highest levels and needed treatment.

This device saved my 4 kids lives and mine. I do not think 5 stars are enough.
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on May 6, 2017
My old unit needed to be replaced, since it had been 6 years since being made/installed, and was beeping to be replaced. Although this is the SAME MODEL NUMBER (CO400), there are slight but very annoying differences. For example, the battery compartment is on the back of the unit, not the front, meaning that when the battery runs low and needs to be replaced, you'll need to take off the whole unit to do it. (The old one had the battery compartment accessible from the front). Also, it used to take 2 AA batteries, now it's a 9-volt. Not a big deal, but AA batteries are generally more abundant in my house. And finally, and most annoyingly, the holes for the screw mounts are further apart. Meaning that the holes/screws I currently have in place from my old unit cannot be used for this one! So now I have to screw a third hole in my ceiling to mount the new unit. That's not only annoying, it's really inconvenient, especially given that I ordered the same unit model number for a reason.
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