The M314 Motion Tracker is a simple surveillance device originally designed for use by rescue and police services, but is widely used by the Colonial Marines. Essentially, it is a high-powered ultrasound scanner that uses doppler-shift discrimination to filter out moving objects from stationary background.
A moving object is shown on the tracker's display as a series of contours of probable loci, with the range and bearing given to the target. Motion trackers are often employed for perimeter surveillance, able to monitor movements of small animal-sized targets up to a range of 1000 metres in open country. The greatest advantage of the motion tracker is its ability to scan through objects; however, intervening terrain can cut this detection range quite drastically and in built-up areas the presence of walls and partitions can reduce the range to less than 20 metres.
Motion tracker operators must become familiar with their limitations. First, they are active sensors, emitting thousands of high-energy ultrasound bursts every second, and can be easily located by enemy fire. Secondly, the tracker range gate function is calibrated to reject small or slight movements (such as bugs crawling, plants waving in the wind etc.), so that very slow-moving objects can infiltrate a tracker's detection cone (as guerrillas did on many occasions during the Arcturan War). Thirdly, trackers are vulnerable to spoofing by ultrasound jammers, or 'jumping jack' decoy devices. As a result, most commanders prefer motion trackers to support other surveillance techniques.
- Aliens: Infestation [Nintendo DS]. WayForward Technologies and Gearbox Software.