The negative reviewer mentioned that his sounded like the batteries were running out of it, but when that happens to mine, it's because the batteries are low! He's either got a defective product or defective batteries. I do agree with the other positive reviewer about how it will sometimes go off with a light change, but oh well! I keep my lights on during the day anyway. It works great to let me know when someone is entering/leaving my office. It works so well that I'm buying another one for my office I go to once a week!