ACSI 1335-1 DPS Standard mortise, SPDT, NO/NC contacts

It works magnetically. The ACSI 1335 sensor body mounts in the frame and a magnet mounts in the door; as the door closes, the magnet comes into proximity and the contact changes state. There is no mechanical plunger to wear out, so the door leaf only has to align the magnet with the sensor.

SPDT means single pole, double throw, so the 1335-1 gives you both a normally open and a normally closed contact off one common. You pick whichever leg your alarm panel, access control board, or door prop timer expects, and you don't need a second sensor to get the opposite state. That flexibility is why the SPDT version gets specified when the panel input convention isn't settled at the time of order.

Mortise. The 1335-1 is the standard mortise DPS, meaning the sensor is drilled into the frame and the mating magnet into the door edge so the assembly is concealed once the door is hung. If you can't drill the frame, or you're retrofitting a hollow metal frame that's already finished, a mortise contact is the wrong choice and you want a surface mount contact instead.

It's a two piece system. The sensor half goes in the frame and a separate magnet goes in the door, and both halves have to be present and aligned for the contact to read a closed door. Plan the prep for both sides of the opening before you start drilling.

Not the magnetic version. For hazardous locations ACSI offers pneumatic models in the same 1335 door position sensor family, and that is what you should be specifying there rather than the electrical contact version like the 1335-1.

It tells the system whether the door leaf is physically closed, which is separate from whether the lock is locked. That single input drives door forced open alarms, door prop alarms, relock on close after a valid card read, and status reporting back to the head end. If you're monitoring an opening for anything beyond the credential itself, the 1335 sensor is the part supplying that state.

Commercial. The 1300 Series door position sensors are catalogued as commercial electronic access control hardware, which is the class of DPS used on monitored egress doors, stairwell doors, and card reader openings in institutional and multi-family buildings.