A laser diode, (LD), injection laser diode (ILD), or diode laser is a semiconductor device similar to a light-emitting diode in which the laser beam is created at the diode’s junction. Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination.

This Keyes device is one of the most common devices found in Arduino sensor kits.   Coupled with other components, it can be used to create trip wires or optical effects.

The laser diode sensor is particularly neat because it can be directly powered from an Arduino output pin as it only draws 30 mA from the processor that has outputs rated for 40 mA.