Install a relay that voids UL listing?; Shunting out a garage door

Q: I was asked by the fire chief of one local town to install a relay with dry contact closure onto the 120V smoke detector system in the town library. There is already in place a 4-channel digital communicator for the library’s wireless call buttons, with three channels available. The fire alarm system is, of course, local and consists of 120V detectors and several pull stations throughout the building. Any suggestions?

A: Yes, walk away from the job. Let me be a little nicer and explain. The fire chief needs to understand that he is asking you to void the UL listing on this device by modifying it. If nothing else, consider the liability to do a job like this.

While I am sure you could jury-rig the device, the smoke detector was not designed for this modification. There are models available for what you want to do. Inform the fire chief that you will be glad to install the correct model for the application.

Q: Do you know of a simple way to shunt out a customer’s garage door?

A: You can connect a relay to the light output of the garage door opener. When the automatic garage door is activated, the relay contacts will shunt out the overhead door contact. Make sure that the delay time on the light is set long enough to allow plenty of time to enter the garage with the car.

Whenever configuring an option like this, you will want to discuss it with the customer and make sure that false alarm prevention measures have been taken.

If you have any tips to share or have questions about installations or troubleshooting, E-mail Security Sales & Integration Contributing Technical Columnist Bob Dolph at

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