The Omron D4SL-N4FFA-DN is a guard lock safety-door switch — a solenoid-locking interlock that prevents access to a hazard zone until the machine controller signals a safe state. The mechanical lock holds the guard closed; the 24 VDC solenoid releases it only when power is applied, so a power loss keeps the guard locked (fail-safe). Built-in switching contacts are arranged as 2NC/1NO + 2NC, giving two normally-closed channels for the safety circuit plus one normally-open auxiliary for status feedback. The orange LED indicator on the 24 VDC version confirms solenoid power is present.
The switch body has an M20 conduit outlet for cable entry, and the connection method is via a connector (not hardwired), which speeds replacement on the line. The head is resin; the standard release key is metal. This is a safety-rated interlock for guarding machine access points — press doors, hinged guards, or sliding gates where a trapped-key or solenoid-lock is required by the risk assessment.