The Honeywell 7939-2 is a surface mount door contact and window contact that can be used with any wired alarm control panel.
The 7939-2 is similar to the 7939WG door and window contact. However, even though they look the same, the 7939-2 has an important feature that distinguishes it from the 7939WG. While the 7939WG is a Form A, SPST, normally closed contact, the 7939-2 is a Form C, SPDT, normally open or normally closed contact. You can connect this door contact to a normally closed or normally open contact circuit. There are (3) terminal screws on the 7939-2 so that you can wire it to your zone circuit. Use the ‘NO’ and the ‘C’ terminals for wiring to a normally open contact loop and use the ‘NC’ and the ‘C’ terminals for wiring to a normally closed contact loop. Both contacts use an internal reed switch with a rating of 100mA at 28VDC.
You will need to surface mount your Honeywell 7939-2 when installing your door contact or window contact. The contact should be installed on the door or window frame and the magnet should be installed on the door or window so that when the door or window is closed, the magnet and contact are flush and in close proximity. In fact, the 7939-2 has a magnet gap of 1” so the contact must not be further from the magnet than 1” when the door or window is closed. You can install the surface mount contact in almost any application as it has an operating temperature of -40° F to 194 ° F.
The Honeywell 7939-2 window or door contact includes spacers, covers and mounting screws in addition to the contact and magnet. You can use the spacer to flush mount the contact to the magnet when your door or window frame is not flush with the door or window. The cover will conceal the wiring connections and the end of line resistor (EOLR) if you choose to install the resistor at the device instead of inside the alarm control panel.