I'm new to electrical wiring. I understand circuits, soldering, and basic wiring in parallel / series but calculating and understanding draw, resistance, etc. is new to me.

That being said, I have two of these http://www.lowes.com/pd_690400-41277-3320-L___?productId=999925302&pl=1&Ntt=iris in my garage...

Here is a photo of what they look like: Iris Door/Window Sensor

I have tons of varying output AC-to-DC adapters that are not being used for anything and was wondering if I could somehow solder wires to the battery terminals of these two sensors and wire them to a single AC-to-DC and plug it into my garage wall outlet so I don't have to worry about batteries.

The battery that comes with them is a single CR2 3V lithium battery.

I suppose my question is, what rough estimate voltage output would I need to power two of these in parallel I guess? or would I wire them in series?

Any advice you can offer is very helpful!

  • \$\begingroup\$ I'd just like to point out that this kind of device, equipped with a lithium cell, could probably operate for decades without changing the cell. 3VDC is also a somewhat uncommon voltage to find in a wall power adapter. I've only seen one in my life, and it was not regulated. So all that to say, eliminating the batteries in this case may be a lot more bother then is practical. \$\endgroup\$
    – Randy
    Commented Feb 3, 2016 at 21:33
  • \$\begingroup\$ Is this contact sensor is part of your burglar alarm system? If your alarm system has been professionally or correctly installed it will have a backup battery capable of supporting the system for 24 hours if the mains supply fails. If you power your contact sensors from the mains it means that at least part of your property is no longer protected when the mains fails. Also, if the mains supply fails then your alarm panel may give out a warning bleeps because it has lost the supervisory signals from the contact sensors. \$\endgroup\$
    – Steve G
    Commented Feb 3, 2016 at 22:04

1 Answer 1


A 3V DC adapter would be appropriate. Wired in parallel. Make sure it is a regulated 3V adapter (measure the voltage of the adapter without a load, if it's 3V, you're fine), many old/cheaper AC-DC converters are unregulated, and will produce a much higher voltage when not used with the equipment they are designed for.


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