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!
the first one i got didn't work out of the box. i tried two completely different sets of batteries and couldn't get a sound out of it.
the kind that has two pieces, one that mounts to the door frame and one thst mounts to the door and chimes when the door opens (based on magnets instead of motion/light?) seems better; less likely to false alarm. but staples doesn't have that choice so I am going to return and re-order and cross my fingers.
I bought this for work as we have a conference room with no windows and when we are in mtgs we don't know when someone comes into the office. At first I was very satisfied because it did exactly what we needed. Then after about 30 mins we got annoyed with it due to it will go off if there is a shadow or even something that can reflect in it's path. I've tried putting paper in front of it and moved it everywhere, and I get the same result each time. So good thing is that it DOES work, bad thing is you never know if it's a customer or just a reflection or shadow.