Abstract: The security apparatus is mounted to objects to indicate when a person or moving body is in the vicinity. Detection of movement or vibration is determined by air bubble movement in a liquid charged chamber. Light emitting means radiating from end placements of the chamber cause lateral reflections from the end edges of the bubble. Detecting apparatus senses the differential in received bubble edge illumination and activates security warning equipment when there is imbalance due to bubble movement. Bubble dimension changes due to temperature variations are nullified by balance sensing. Automatic sensitivity control by sensing ambient light or under timer control allows security maintenance over changing environmental backgrounds. Remote supervision by radio link is an embodiment. Security of the radio communication is maintained by a process of carrier frequency division used for self modulation of the carrier frequency signal.