Review on Combination Monoxide Detector Operated CST503（2 by Geoffrey Graham

I bought these to replace 10 year old carbon monoxide alarms that no longer work. As a bonus I got these which also have a smoke detector. When they go into alarm mode they are loud but not overly loud and the LED will flash as advertised. The reason for the two stars is how long it took for them to actually sound the alarm. I put a plastic bag over my car's exhaust pipe to test for carbon monoxide function. The alarm took much longer than I expected to sound. They didn't really sound the alarm until they came out of the bag a few minutes later. A few days later the detector was in the garage. I started the car and backed up, a few minutes later the family heard the alarm go off. The garage was open all the time, the car's exhaust was on the garage door, and the alarm was on a chair 25 feet away. It's not clear why it worked, but not when it was in a bag attached to the car's exhaust pipe? To test the smoke, I burned the wire. (This is a common NFPA testing method.) As you can see from the attached photos, they were exposed to a lot of smoke before they sounded the alarm. In fact, by the time the alarm went off, soot had accumulated on the detector cover. We're concerned they aren't sensitive enough to give you enough time to move away in the event of a fire or carbon monoxide alarm. Also, I don't see any UL listed detectors which are required in many areas. Bottom line, my test wasn't scientific in any way, but the device didn't meet my testing standards. I gave two stars because both the CO and smoke set off an alarm.