The motion trackers were made by Terry Reed. The basic shell of the tracker is a power drill casing. The trackers were dressed with mostly photographic accessories.
Component parts of the motion tracker
The tracker which appeared in the Aliens Technical Manual was a copy made by Terry Reed for Lawrence Nathan of Fiction & Fantasy Models in North London in early 1990. Resin casts of this were made available and the tracker in this collection is an adapted version of one of these. Many of the resin parts have been removed and replaced with the actual items.
The display unit on the side of the tracker is an original from the film. It is a Hama slide viewer.
For long shots of the trackers a simple blinking light was fitted inside the screen box. Insert shots of the screen display were made possible by using a small TV monitor, shot directly end on to disguise the length of the unit, which can be seen briefly during the scene in which the marines first use the trackers in the colony complex.