A corner sensor assembly includes a housing having at least one magnet attached thereto, wherein the magnets allow the corner sensor assembly to be readily attached and relocated to corner structures within a building. The assembly includes at least one motion sensor for detecting motion within two opposing fields of monitoring. At least one visual indicator is activated when the motion sensors detect motion within both fields of monitoring and are deactivated when no motion is sensed in at least one of the fields of monitoring. The assembly includes an integrated power supply located within the housing.