Whereas the motion sensor is handy for those in the van to check the ghost’s location, the infrared light sensor lets those already in the house know where the ghost might be.

Why Your Smartphone Needs an Infrared Sensor You could use a heat sensor to check your house for leaks, for instance. But mostly, it's a lot of fun.

The IR sensor array, which on the palm-sized vehicle consisted of just a handful of components, evolved into a PCB-backed bar nearly 0.5 meters wide. Potentiometer tuning was a fiddly affair, but ...