ACSI 1335-4 Door Position Standard mortise, DPDT, NO/NC contacts

It works magnetically. The switch body mortises into the frame and a matching magnet mortises into the door edge. When the door swings shut, the magnet comes into proximity with the sensor and the contacts change state, so your panel sees door closed. Swing the door open and the magnet leaves range, and the contacts revert. There is no physical plunger to wear out or get jammed by a warped door.

DPDT means double pole, double throw: two independent switched circuits inside one sensor body, each with both a normally open and a normally closed side. That gives you two isolated outputs from a single door contact, so one set can report door position to the access control panel while the other feeds an alarm panel, a door prop timer, or a BAS input. The NO/NC choice is just which side you land on at the terminals, depending on whether your input wants a closed loop or an open loop when the door is shut.

Mortised. The 1335-4 is the standard mortise version, so the frame has to be drilled to accept the sensor body and the door edge drilled for the magnet. If you are retrofitting hollow metal frames already in place and cannot get to the frame face or run a fresh wire down the hinge jamb, budget install time for that, or specify a surface mount contact instead.

Not this one. The 1335-4 is the standard magnetic mortise model. ACSI also builds pneumatic models in the 1335 family specifically for hazardous locations, and that is what you want where a magnetic switch is not acceptable. Sort that out before ordering, because the two are not interchangeable in the same prep.

Yes, and that is exactly the job the 1335-4 does. A mag lock tells you it is energized, not that the door is shut, and a REX only tells you somebody pushed to leave. A door position sensor is the only device on the opening that confirms the leaf is actually closed, so it is what drives door-forced and door-held-open alarms and what lets the panel relock cleanly behind a valid exit. The DPDT contacts mean one sensor can serve both the access panel and a separate alarm input.

The 1335-4 is a two-piece assembly by design: the magnetic sensor mounts in the frame and the magnet mounts in the door, and the sensor only reports position when both halves are in place opposite each other. Confirm both pieces are in hand before you cut the frame prep.

Commercial. The 1335 sits in ACSI's 1300 Series of electronic access control hardware and is specified for commercial openings, the kind of doors already running a card reader, mag lock, or monitored egress point. For a house alarm you would use a residential reed contact instead.