Abstract: A security system for an opening such as a door, window, or the like wherein the opening is defined with a generally planar orientation having at least a pair of generally diametrically opposed corners, the system including light transmitters arranged in the vicinity of at least one of the corners emitting light from the one corner within an angle limited by the sides of the one corner, the light being directed across the opening in a direction toward the other of the corners, and light receivers for sensing light emitted from the light transmitters, the light receivers being arranged on at least one of the sides of the opposite corner. In one aspect of the invention, the light transmitters are arranged in the vicinity of only one of the corners and the light receivers are arranged on both sides of the opposed corner.

Abstract: An Alarm system for furnishing an alarm signal in response to unauthorized entry through a passage connecting the outside to the interior of a building, wherein a first detecting device furnishes a first output signal when sensing the presence of a person in a first portion of the passage. A second detecting device nearer the outside of the building furnishes a second output signal when sensing the approach of a person. An evaluating circuit receives the output signals and initiates an alarm signal only if the second output signal is furnished prior to the first output signal.