Connect a Siren Strobe or Strike to a Relay and Power Supply

If you need to trigger a siren, strobe, or other device using a relay, you'll need to provide a power supply with enough capacity to run the siren and ensure you have a relay rated with sufficient capacity.   The relay may be built into some other electronic device like an intercom system or driveway alarm for example.  Check the specs on the siren - it will typically be rated 12VDC and some amount of "amps" or "milliamps".  Typically a siren will be in the range of 500mA to 1.2 Amps.   The power supply will need to have the same voltage, and the Amps rating of the power supply should be greater than the need of the siren.  For example to power a 800mA siren you'll need a 1A power supply.  For a 1.2A siren you'll want a 2A power supply.  Always choose a supply larger than the maximum power draw of the siren or device you are powering.

1. Connect the positive (+) terminal of the power supply to the common (C) connection of the relay
   
2. Connect the normally open (NO) terminal of the relay to the positive (+) terminal of the siren
   
3. Connect the negative (-) terminal of the power supply to the negative (-) terminal of the siren

If you are using more than one siren, connect additional siren(s) in parallel to the first connection.  In this case you also need to use a power supply with a larger AMPS rating but same 12VDC voltage.  If you have 3 x 1A sirens you'll want a power supply rated greater than the sum, which is 3A.  These are most often found as 12VDC 5A power supplies.

In the case of two sirens it would look something like this.  The idea is that the normally open connection goes to the positive (+) connection on both sirens, and the negative power supply connection goes to both negative (-) connections on the siren.

Note: An inductive load like a door strike will likely need some sort of 'snubber' connected to protect the relay contacts from welding themselves shut from the arcs/sparks that may happen when a relay switches an inductive load.

As always, when in doubt STOP and ask for help before connecting wires that may damage these delicate devices. 

• Related Articles

• Connect 120V wired smoke detectors to security alarm system like DSC, Vista, Concord

  We are often asked how to add 120V wired smoke detectors to a low voltage security alarm system like DSC, Vista, Concord or Elk. First we need to point out that smoke detectors are a life safety product and so it's critical that you read and ...

• Power supply for Ring pro

  If they are using plug in AC transformers for alarm systems, the Ring Doorbell will short out the power every time the doorbell button is pressed which will cause the transformer to blow the internal fuse. Your best option is  to buy plug in power ...

• Expanding Security Alarm System Power Supply

  Wired Security systems (eg DSC, Elk) are powered by an external power supply, and then in turn they supply power to 12VDC peripherals such as keypads, zone expanders, motion sensors, glass breaks, smoke detectors. This auxiliary power from the panel ...

• Wiring RC840T-120 Relay

  The Aube / Honeywell RC840T-120 relay provides two functions: Provide 24VAC power on the C and W terminals to power a low voltage thermosat Switch the 120V circuit when triggered by the low voltage R & W terminals Take care to ensure you are not ...

• Problem with DSC Keypad Power or Devices Won't Power

  Keep in mind that DSC Powerseries wired alarms can provide up to 700mA current to connected devices.  While this is typically sufficient for multiple keypads and zone expanders, it is important to make sure this limit is not exceeded.  The newer LCD ...