Multiple input/single output 110V AC signal - Will a power relay work???

Thread Starter


Joined Jul 29, 2021
I have a small facility with multiple rooms, each of which is equipped with a sensor alarm that run independent of one another, all are 110V AC. If the alarm is triggered in one room only that room will alarm. I need to install an outside alarm that will sound if any of the 4 rooms are triggered while still keeping each room independent. Currently, each alarm works perfectly. If I tie into each of the rooms hot wire then tie them back together at the outside alarm, it will either trigger all the alarms or create a loop and trip the breaker (not sure). I thought I could use a relay like this Problem is I do not know if this would actually work or if there is another device I can use. Essentially what I need is a 'check valve' for 110V AC electrical so I'm a bit lost. Below is the layout. Blue boxes are the smart plugs that will switch on if triggered, the red ovals are the alarms (plugged into the smart outlets). Green lines represent tying into the wiring to the alarms so it would energize the outside alarm. Any advice would be greatly appreciated.

Thank you.
Alarm Layout.JPG


Joined Jul 29, 2018
You would need 2 of the (dual) relay kits you've identified above to do the job. Each of the four relay coils is wired in parallel with one alarm and, using one normally open (NO) contact pair per relay, wire the four NO contact pairs in parallel. Use the paralleled contacts to switch power to the chosen load. But the relays need to be housed in a proper enclosure such that electrical safety concerns are addressed. Not really a safe project for an inexperienced builder.


Joined Dec 2, 2017
Those relays are expensive, I would look for a less expensive component such as an opto to interface with the existing alarms, then parallel them to drive a single power relay for the outdoor alarm.


Joined Nov 6, 2012
Here is how to wire the Solid-State-Relays that I suggested ...............
If any Alarm turns on in any room, the Outside-Alarm will also turn-on.
There are no "polarities" to be concerned about, just Inputs and Outputs.
The Outputs are effectively just like a standard Light-Switch, and rated for up to a 15-Amp-Load.
Fire Alarm Network FLAT .png