The motion detector and glass break detector are very useful devices and play an essential role in any home security or commercial alarm system. The motion detector when used correctly is a sure and immediate detection device that will cover a lot of area effectively. For instance you may have a large room in your home or at your business that has many windows. These are easy points of access and need to be protected. Rather than put a sensor on each window you can put one motion detector in place to cover each window and save quite a bit of money. Of course if you have pets at home you will want to be careful of false alarms. Be sure and get a motion detector with pet immunity that will compensate for the weight of your pet. You may also want to consider whether or not you will arm your alarm system while you are in the premises. If so, keep in mind that the motion detectors will automatically bypass when you arm your alarm system in the "stay mode", allowing you to move about freely. This leaves you unprotected if you are using motion detectors to cover the perimeter. In this case you could use a glass break detector to cover the windows. A glass break detector will arm while in the stay mode, will let you move about freely and will trip when a burglar breaks the glass to unlock your window. Most glass break detectors will cover areas of around 15 feet to 25 foot radius's. Be sure and check the specifications of your glass break detector or motion detector before you place it.