Think of the tattletale Border Guard as an invisible 80 foot perimeter of protection. It is a PIR (passive infrared motion detector) that detects heat energy 40 feet from each side. Dual Beam Motion Detecting Technology ensures that there will be no false alarms! The Border Guard Sensor can be placed up to 3000’ from the tattletale base unit, and it’s durable tamper proof design makes it perfect for use outdoors!