To access the switch, unsnap and slide off the back cover as shown in Figure 1, exposing the battery, lead wire screw terminals, and digital coding switch (see Figure 2). Figure 1. Removing the Transmitter Back Cover SCREW TERMINALS CODING SWITCH Figure 2. 9- VOLT BATTERY Transmitter Components CODE SETTING CAUTION! All transmitters and receivers must be re-coded by installer prior to operation. DO NOT USE THE FACTORY SET CODE! Among the 256 possible codes, considered invalid, and should not be

Each transmitter can perform many remote switching tasks and are typically used in wireless/hardwire security systems. Each unit is powered by a self-contained 9-volt battery and can be connected to various sensors with the built-in screw terminals. NOTE: Transmitters with a /K model number suffix are Linear’s Canadian models tuned to 318 MHz. These instructions pertain to both the /K and standard 303.875 MHz U.S. models. D-21A N/O TRANSMITTER The D-21A is used with various types of security sen

CODE SWITCH LOCATION The digital coding switch is attached to the circuit board inside the case. To access the switch, unsnap and slide off the back cover as shown in Figure 1, exposing the battery, lead wire screw terminals, and digital coding switch (see Figure 2). Figure 1. Removing the Transmitter Back Cover SCREW TERMINALS CODING SWITCH Figure 2. 9- VOLT BATTERY Transmitter Components CODE SETTING CAUTION! All transmitters and receivers must be re-coded by installer prior to operation. DO N

The operator may have only two terminals or the numbering sequence may be different. TO CONNECT A THREE-TAB RECEIVER: 1. The push on receptacle on each wire is connected to the straight tab of the receiver terminals. 2. Each terminal is marked on the data label on the back of the receiver. Connect the wires to the receiver terminals as follows: a. Receptacle with two wires (power transformer and push button wire) to terminal mark “1 ” or “24V”. b. Receptacle with second push button wire to