The Siemens 3SF78426BD11 is a light curtain host receiver with a resolution of 1, used as the receiving end of a safety light curtain system that guards a hazard zone by detecting objects — typically hands or fingers — reaching into the protected area.
As a host receiver, this unit pairs with a compatible emitter to form a Type 4 safety light curtain per IEC 61496-1/2, suitable for guarding machine access points where a 14 mm resolution (typical for finger detection) is required — though the exact resolution should be confirmed against the system's datasheet for this specific model.