The Siemens SIRIUS 3SF1234-1LC05-1BA1 is a mechanical safety switch with positive opening contacts — the kind you wire into a guard-door circuit so that when the door opens, the NC contacts physically break before the actuator reaches the safe position. Two safety-related NC contacts give you a redundant pair for SIL/PL-rated stop circuits; no NO auxiliary contacts on this variant. The 24 V LED gives a quick visual on the AS-Interface bus power without needing a multimeter.
Mounts in any position via screw fixing. The block narrow plastic housing is 31 mm wide — fits a standard 30 mm cutout or DIN-rail adapter plate. IP65 means it handles washdown spray; fine for food or packaging lines where you hose down the guard enclosure. The M12 plug carries AS-Interface and ASIsafe on pins 1 and 3; pin 2 and 4 are unused, so a standard 4-pin M12 cordset works but you only need a 2-wire ASi cable if you're running the bus separately.
Surge voltage resistance is 0.8 kV, so it's not for direct mains switching but fine for the 24 V control circuit it's designed for. Mechanical life is 15 million cycles typical — that's a lot of guard-door openings before the spring wears out. Repeat accuracy of 0.1 mm matters when the actuator position needs to be consistent cycle to cycle.