A solar powered perimeter beam security system comprising a plurality of spaced towers. The towers have detection beams extending between them for detecting an intruder when at least one of the detection beams is interrupted. Each of the towers communicates with a remote unit. At least one of the towers is movable from one location to another. An alarm. The detection beams define an intruder detection area into which an intruder cannot pass without breaking at least one of the detection beams thereby setting off the alarm. The detection area is expandable and decreasable by moving at least one of the towers. The towers are incapable of movement without setting off the alarm once positioned with the detections beams being activated.