A Motion Sensor is a security device used to detect movement and trigger an alarm system (either local or central) in order to alert the immediate personnel in an area. In the Splinter Cell series, Motion Sensors appear in different forms with different functions, depending on the game mode and actual gameplay.
Motion Sensors appear in the solo campaign sections of Splinter Cell: Pandora Tomorrow and Splinter Cell: Essentials. It appears as a red circle with a silver outline and reflective surface attached to the wall. It can't be removed, disabled or destroyed by the player. The only way to bypass Motion Sensors are to sneak past them very slowly. They will stop beeping once the player is away from them, if they begin emit rapid beeping sounds, it indicates that the player is currently moving too fast. Triggering Motion Sensors will activate an alarm system, bringing enemies in the level into a more alert status, with changes depending on the alarm level.
Motion Sensors appear in multiplayer modes Spies vs Mercs as a device that is used by Mercenaries to detect movement; it detects quick and fast movement from Spies. It detects movement infront of Mercenaries, however, it cannot detect movement behind them. If a Spy has silenced boots equipped, they will not be detected by the Motion Sensor. Slow movement will not be detected by the Motion Sensor as well. The Motion Sensor does not identify what level the movement is coming from.