The anti-personnel sensor is a device that measures the electromagnetic fields and heartbeat of nearby human life forms and reports their presence to the user via vibrations.
In military use, the anti-personnel sensor can detect an enemy's presence without betraying the user's position. The closer a detected body is to the sensor, the stronger the vibration that is emitted. The sensor can also detect hidden, unmoving enemies. However, its lack of accuracy makes it difficult to reveal the exact position of detected bodies. The sensor is not dependant on radar and is therefore unaffected by interference fields created by chaff.
An early model of the anti-personnel sensor was used by FOX operative Naked Snake during both the Virtuous Mission and Operation Snake Eater, in 1964. Though its use was limited by batteries, its focus on human detection and resistance to electronic jamming gave it an advantage over the motion sensor and active sonar.
Behind the scenes
The AP Sensor was introduced in Metal Gear Solid 2: Sons of Liberty, in which it is included within the player's inventory by default. The device operates by vibrating the player's game controller when equipped. Using the sensor, however, disables all other vibration-feedback in the controller. When used in First Person View, it will only scan in the direction that the player's character is facing. The Trial Edition demo for the game identifies it as the "V sensor" in-game.
- "AP Sensor.
Sensor detecting lifeforms. Rumbles on enemy approach. All other Rumbles will be OFF when sensor is activated."
- ―AP Sensor description from Metal Gear Solid: The Twin Snakes.
The AP Sensor was later included in the Metal Gear Solid remake, The Twin Snakes. Rather than appearing in the player's starting inventory, it can be procured within the pool of the cargo dock at the beginning of the game.
The device makes an appearance in the prequel Metal Gear Solid 3: Snake Eater, where it also emits an audible beeping sound while in use. It weighs 1.5 kg when placed in the player character's inventory. The sensor is not usable on European Extreme difficulties.