You are absolutely right. There are standards that should be followed and the WTMD's are tested daily to ensure they are working properly and if they aren't, they are to be taken out of service until the maintainence contractor can inspect them. That being said, I have noticed that while I never alarm, I can walk through one mag on my checkpoint and get "3 stars" and walk through another and get "4 stars." They all pass when we test them, that's what counts.