The RUST Laser Detector is a deployable electrical gate (trigger) device that allows for electrical current to pass through while a player stands in the beam that it emits. If you picture a standard electrical Switch when a player is standing in the laser beam, the light would be on and when no one is standing in the beam, the light would turn off.
Laser detectors are one of a series of implements that players can use to trigger electrical events and are pretty popular in the application of trap bases. The device itself can be placed on most surfaces but is most effective when pointed from one wall to another.
Laser detectors are found in an assortment of low-to-mid-tier crates, as well as dropped from many scientist types. RUST players may learn them directly or through a Scrap investment into the Tier 2 Workbench tech tree.