We can use them to cut things, create laser light shows, and also as a rangefinder.[Ignas] wrote in to tell us about [Berryjam’s] AMAZING write-up on creating an Arduino based laser rangefinder.

On the inside, an infrared LED and a photodiode are arranged in a way that allows no direct light ... wiring the dust sensor to the board and taking the enclosure out of the laser cutter ...