D-21A: Normally Open Wall-mount Transmitter

The Nortek Security & Control Family of Brands

The Model D-21A Normally Open Wall-mount Transmitter has a normally open input circuit that operates in conjunction with an externally mounted normally open magnetic or mechanical contact. When the external contact closes, the transmitter automatically transmits a two-second digitally coded signal to a companion standard digital receiver. Pressing the test pushbutton on the front of the transmitter will also cause the transmitter to send a signal. Each transmission causes the red LED indicator on the front of the transmitter to light, showing that the transmitter is sending a signal and that the battery is in good condition.


  • Slimline case design
  • Test/operate switch
  • Test/operate LED
  • 2-second transmission
  • Standard digital format: 256 selectable codes
  • One N/O input loop circuit
  • Loop input screw terminals
  • Powered by one 9-volt battery (included)
  • Current consumption: 12 mA transmitting
  • RF frequency: 303.875 MHz
  • 2.4″ W x 4.7″ H x 0.9″ D
  • Order number: SNT00004

Installation Manual

WARNING: Cancer and Reproductive Harm - www.P65Warnings.ca.gov

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