Look at your premise and decide where the valuable items are located, and where the vulnerable points of entry are located. Then think about where the like traffic pattern area where the burglar will walk by are located. For example in a small cape home, your may decide to place a motion detector on the outside wall in dining room that looks into the kitchen and also covers the rear entry door into the kitchen. A second motion detector may be placed in the front living room that covers the front entry door, and the bottom of the stairway that leads to the second floor. A good mounting height of the infrared detectors is 6 to 8 feet above the floor. Avoid placing the detectors in an area that will be looking directly into a stove, fireplace, of fan. Avoid placing a detector in a area that looks directly at an outside window.