I was skeptical at first whether such a cheap device also good enough now. After unpacking I want it to hang. For those with ordered magnetic disks is too heavy (3 AA batteries). It slipped from now. I had to fix it with screws. And it really did not matter, except that occasionally flashed the green LED. Will it really give alarm if needed? So I went into the garage. After a short time a value appeared on the display. When I then started the car, I had not only engine noise, but the indicator rose to 999 and put the thing going. It was no longer calm about the test-rest-button. Only the pan in fresh air lowered the value, and then I was able to reset the alarm. I've had the machine two months in use and until now no false alarm. I'm going to buy myself extra equipment for other locations.
Postscript Even after nearly a year of operation I had no false alarm. Only the battery-change indicator is used to. "Praise" will be displayed and every 30 seconds there is a noise as if a bird screams again. When she came for the first time at night, I thought my cat had dragged a bird that beeps from time to time.
