I thought Aleks was kidding, but that UFO thing is in fact $87...
Here is a modern version, it seems:
https://www.amazon.com/UFO-Detector-magnetometer-interfaced-microcontroller/dp/B000FVUKKO
As an alternative, commercial UFO detectors are already available:
https://www.amazon.com/UFO-Detector-magnetometer-interfaced-microcontroller/dp/B000FVUKKO