Summary

TrackIR 5 headphone tracker powered by AAA batteries. Can be tilted up towards the camera.
Fusion 360 files included so that it can be adapted to different headsets.
Works very well.
There are other types of head trackers available that uses an ordinary webcam and free face recognition software. I guess they isn’t as good but probably best to try that first before buying a TrackIR 5.
Battery discharge diagram included.
Batteries in series 2x1.2=2.4v
One resistor and one led in series connected to the batteries.
One resistor and one led in series connected to the batteries.
One resistor and one led in series connected to the batteries.
I soldered the resistors directly to the LEDs.

Use the camera on your phones to see the invisible IR light.

Parts list:
IR Led: 3x SFH485P (Flat side = Long lead = -)
Resistor: 3x33 Ohm ¼ Watt (I used 22 ohm => 6.5 hours, 33 Ohm will last longer)
2 AAA reachable batteries. I recommend IKEA 700mA and their charger. Good stuff.
3 M2x12 screws
Thin wires. My cables plastic outer diameter ~ 1.3mm (AWG 0.25)
Thicker wires for the battery compartment.