The Omron D40R-SPB-21-05 is a magnetic reed switch configured as DPST/SPST, falling under the Specialized Switches category in the Reed, Hall-Effect, & Magnetic Switches subcategory. This class of switch is typically used for position sensing on doors, gates, or safety guards in industrial machinery — a non-contact magnetic actuator triggers the reed element, providing a dry-contact output to a PLC or safety relay.
As a magnetic reed switch, the key selection parameter is the contact configuration: DPST (double-pole single-throw) or SPST (single-pole single-throw) determines how many independent circuits it can switch. For a safety guard interlock, DPST allows one channel for the safety circuit and one for status feedback to the controller.