It's very possibly a quality control issue. The design of the alarm will work so if you're lucky enough to get a well build one with working components you're

It's very possibly a quality control issue. The design of the alarm will work so if you're lucky enough to get a well build one with working components you're in luck. The problem is not being able to rely on them, if you've a lucky one which passed your test are you confident it'll still be working in a couple of years?