This Aliens-Style Motion Tracker Replica Actually Works

The Alien franchise lost its way sometime over the last 35 years and even Alien: Earth seems to misunderstand what made the first two films so good. Though they did it in very different ways, both Alien and Aliens slowly built tension with a foreboding atmosphere and just enough information to let the viewer’s imagination run wild. The handheld tracker in Aliens was a perfect example of the practical implementation of that philosophy, which is why it is a popular replica prop build. But Rob Smith went the extra step and created an Aliens-style motion tracker that actually works.

The tracker scene in Aliens is a masterpiece. Our heavily armed heroes, including Private Hudson as iconically portrayed by Bill Paxton, have handheld radar trackers that can detect the xenomorphs. The trackers show that they’re surrounded by the aliens, which are getting closer and closer, but can’t be seen. It turns out they’re in the drop ceiling—yikes!

It is an incredible scene and Smith wanted a tracker that would work in the same way in real life. The secret component in achieving that is a mmWave radar sensor. That technology is relatively new to the maker scene and is very cool. Sensors tend to have a reasonable range of 5-15 meters or so and are quite accurate, with the ability to detect the positions of humans and animals. They also penetrate walls pretty well, so they’re perfect for a project like this.

Smith used a DreamRF mmWave sensor HAT paired with a Raspberry Pi 4 Model B single-board computer. It displays the locations of detected entities on an LCD screen, with graphics like those seen in the movie. Alongside displaying those fuzzy blips, the Raspberry Pi also plays the tension-building radar ping sound effects through a USB audio dongle and speaker. Finally, an IMU lets the device monitor its own orientation to help keep the graphics consistent with physical movement.

Those components all fit into a fairly screen-accurate 3D-printed model designed by DrMoribus on Thingiverse, which Smith modified in TinkerCAD for this purpose.

There were, of course, many hiccups along the way and Smith goes into detail explaining how overcame challenges like improving the range of the mmWave sensor. But ultimately, he succeeded and he even took the functional tracker to a laser tag arena to gain an edge over his opponents. Luckily, those opponents were humans and not xenomorphs.