TL;DR: It's a Vive Tracker bolted to a dummy flashlight, which controls a virtual light source. The flashlight's power button is also an input device, wired to

TL;DR: It's a Vive Tracker bolted to a dummy flashlight, which controls a virtual light source. The flashlight's power button is also an input device, wired to some Digital Input pins on the Vive Tracker.