I have always thought of motion detectors as an interior trap. You can protect all of your doors and windows in your house, but there are ways to get in besides opening a door or raising a window. I have seen people come in from the roof and even someone with a jackhammer go through a brick wall in daylight. There are all kinds of ways to get in a house other than raising a window or opening a door.
A motion detector is designed as an interior trap to make sure if by somehow or some way they get in past the perimeter alarm they won’t go far before they walk past a motion detector. Typically, we want to put it in a hallway leading to the master bedroom or in what I call the crossroads of the south, someplace where you know if a burglar got in he is not going to go far in any direction before the motion detector picks him up. In a commercial application, warehouses have rivets holding the sheet metal in place. A burglar can peel them back like a sardine can and come right on through. Motion detectors are very important in commercial settings. It is best if they are mounted in places that overlook areas such as the shop, interior hallways, computers, petty cash, or even vending machines. I like to say, “When the rat gets in, he is headed to the cheese.” So make sure your motion detector is your trap and you have it set in the right spot.
Years ago, we had false alarms with motion detectors. Unfortunately, they worked too well and if a mouse ran in front of them it would set the alarm off and the homeowner gets called and woken up in the middle of the night. We had a lot of “boy cry wolf” in the earlier days, but with the technology, we have now some of the motion detectors that can be set for different weights, from 30lbs to 100lbs, before the motion will detect. This makes it where if not only one animal but multiple animals are seen the motion detector will still not go off on our commercial-grade motion detectors. It is designed to prevent false alarms but at the same time be that interior trap that you need.