Alien Anthology Wiki
"I've designed this tracking device. You just set it to search for a moving object so. Hasn't got much of a range, but when you get within a certain distance, it will start to give off a signal."
Ash regarding the tracking device[src]
640px-TD detecting movement

The tracking device, also known as the motion tracker, was a surveillance device designed and built by Ash and subsequently used by the crew of the USCSS Nostromo in 2122 in their efforts to destroy the Alien. As its name implies, it was capable of detecting movement and providing corresponding locating information for the user.


"What's it key on?"
"Micro changes in air density."
Ripley and Ash[src]

The tracking device keyed on "micro changes in air density." When motion was detected within a certain distance, the device would begin to give of a signal and the source of the movement would be represented as a dot on the tracker's display. However, the range at which the device could detect movement was short. The tube on the front of the tracker had "ELECTRO MAG FIELD TRACE" written on it.


After a Chestburster erupted from Kane in 2122 aboard the USCSS Nostromo, two tracking devices were constructed by Ash in an attempt to locate the creature. After the destruction of the Nostromo, all known tracking devices were destroyed along with the ship.

Alien novelization[]

In the novelization of Alien, the motion tracker is quite different to the version used on screen. It is far smaller, being only around the size of a "communicator",[1] and it also lacks a display screen. Instead, the device is fitted with a red light that illuminates when movement is detected, and a crude needle gauge to display distance.[2] The tracker is also capable of being silenced via a control, which Ash does when he detects Lambert or Dallas.

Unlike the tracker seen in the film, Ripley notes that it looks like it was assembled in a factory, instead of something "hastily cobbled together in a commercial tug's science lab."[3]

Behind the scenes[]

The tracking device prop was built by Ron Cobb.[4] The main body of the prop is a Panasonic Ranger-505 portable TV with various cosmetics added,[5] including an ice cube tray (left side), a Stadium black plastic 7" gully cover (right side), a 45mm diameter Vernier dial (top), and cut down plastic speaker grills (right, left and back side). The prop also features colored lights, a small television viewer, and a sound output to indicate detected movement. The key used with the prop is from a 1970's Vauxhall car.

At least two props of the tracker were made for Alien, with one currently owned by collector Bob Burns. The tracker owned by Bob Burns is not complete, missing at least one part — the tube that starts to the right of the gully cover and runs in front of the weapon, connecting with the front end of the handle. Strangely, a grill that does not appear in the film was added at an unknown time to the front of the tracker, below the tube.


  • When the trackers are first introduced in the film, they emit a high-pitched humming when they register movement, as heard when they are first tested and when Ripley, Parker and Brett mistakenly detect Jonesy. However, when Dallas is in the air shafts, the devices instead issue a completely different beeping tone.
  • In Aliens: Colonial Marines's DLC map "Nostromo", two unusable tracking devices are seen on the cafeteria table in the middle of the map.


  1. Alan Dean Foster (1979). Alien novelization. Warner Books, Inc., 201.
  2. Alan Dean Foster (1979). Alien novelization. Warner Books, Inc., 205.
  3. Alan Dean Foster (1979). Alien novelization. Warner Books, Inc., 202.
  4. Alien Anthology (2010)/Prometheus to Alien: The Evolution - Alien Anthology Archives - Alien - Post-Production and Aftermath - Miscellaneous - Laserdisc Archives