Perimeter protection is the first line in the defense to detect an intruder. The most common points equipped with sensing devices for premise perimeter protection are doors, windows, vents, skylights, or any opening to a business or home. Since over 80% of all break-ins occur through these openings, most alarm systems provide this type of protection. The major advantage of perimeter protection is its simple design. The major disadvantage is that it protects only the openings. If the burglar bursts through a wall, comes through the ventilation system or stays behind after closing, perimeter protection is useless.