It creates an invisible detection zone; when an object (typically a hand or body) breaks the beams, the safety outputs switch off the machine's hazard within the response time. This is the part you spec when a risk assessment calls for perimeter or point-of-operation guarding on presses, robots, or automated assembly lines.
What the series tells you
The F3SJ series is Omron's slim-profile safety light curtain family, designed for compact machine guarding where mounting space is tight. The series designation alone means you get the standard F3SJ feature set: a 25 mm resolution variant (the "P25" in the code), a 480 mm protected height ("0480"), and a 01TS connector/cable termination. The Bulk packaging means the unit ships individually, not on a reel or tray — expected for a safety device that gets one-at-a-time panel installation.