For a Laser Block to function, at least two of them are required. Place a Laser Block down then place another Laser Block orthogonally to the first within a five-block range. A laser will form between them when set up correctly. Additional Laser Blocks can be connected to the first two in any direction, horizontally or vertically. When a player or mob crosses through one of the lasers, the two Laser Blocks that are connected to it will emit a redstone signal for three seconds.
The Laser Block can accept two different Modules:
Harming Module: Adding this module will cause any lasers emitted from the Laser Block to damage entities that step through the beam.
Whitelist Module: Adding this module to the Laser Block will suppress a redstone signal when players listed in the module cross the beam.