The wife and I wanted a CO detector to replace the old one we bought 10 years ago. Out of interest, these units should be replaced every 6-7 years, some sooner. We have a portable gas fire plus a log burner. We wanted protection in case of a flue leak, or problems with the gas fire. The unit arrived, well packed, easy to use. There are no user-replaceable batteries, so the unit is designed to last the warranty without any intervention, which I think is a good idea. The first thing we did was activate it by removing the plastic pin - this is very easy, and the unit sprung into life. The large button on the front "tests" the sounder unit, and you can switch between room temperature and Carbon monoxide level. The display is large and very clear. The sounder is very loud - sufficient to wake anyone. Next, I ran a full test of the actual unit to see how quickly it would detect dangerous emissions. You can do this by pressing the large button until the spanner icon comes up, then the unit is in test mode. You do not need those canisters or real smoke; I used an incense stick, and held the unit above it. Perhaps you never realised that incense sticks give off potentially dangerous smoke, but don't worry, the quantities here are very small, less than a gas grill, so there is no need to worry! Within about 1 minute you could see the ppm reading rising in the display, and as soon as it reached the trigger level of 50, the alarm went off. In normal use the trigger level is 200 ppm, but the test threshold is deliberately lower, to make it easier to test the unit safely.
In summary, I found it to be an excellent unit, and I know some people have had issues with some CO detectors to trigger off without reason, scaring them, but there was certainly no false triggers with this unit. Besides, if you buy a good unit like this one, you can see the ppm reading, so there is no error. I like the sealed nature of the unit, a Li-Ion battery that lasts a lifetime means you just place it in the room where you want protection, and other than testing it once a month, you simply forget it. Get one, it could save your life.