Adding a contact sensor to a doorbell

I’m trying to get doorbell monitoring capability using an Ecolink door/window sensor with the external contacts. I’ve read about getting an external reed switch and putting it next to the coil for the plunger inside the doorbell unit. I had a different idea, not sure if this would be safe for the sensor or not.

Here’s what I was thinking. My transformer puts out 18.5 VAC measured at the doorbell switch. If I wired it up as shown below, would I risk frying the sensor? Would a resistor inline with the leads to the sensor help? Or should I just get the reed switch?

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Yes. :disappointed_relieved:

Check the quick browse lists in the community – created wiki in the project report section for the “doorbell” list and you’ll see how other people have done it safely.

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If you have an “old fashioned” door bell you may want to check if the vibration of the bell housing is enough to be detected by the movement capability of a Smartthings multi sensor. It works for me.


Thanks guys. So I already bought the contact sensor. It’s either spend a couple bucks for the Reed sensor or get the multi sensor. I can’t really think of another use for the contact sensor at the moment…Any votes for which method is more reliable? It is an old style bell with the plunger that hits the “ding” and the “dong” bars.

I tried your method and the contact sensor didn’t like it. Had to get a reed switch. I think I found one on eBay or Amazon for cheap.

Yes it would.

Check this simple solution to using the Ecolink sensor. I did exactly that until I got a Ring Pro:

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I read your setup earlier in a different thread, isn’t yours a DC transformer? Mine is AC. Also, I measured voltage across those two terminals on my doorbell while the button was pressed and there is no voltage difference, so I don’t think mine will trip a relay.

I went ahead and ordered both a reed switch and a multi sensor. Will try the reed switch first as I’m sure I can find another use for the multi sensor, but if that doesn’t work reliably I’ll try the multi sensor instead.

Love me some Amazon same day delivery, should have them this by this evening.

Oops, sorry about that.

I got both sensors today. Just tested the Reed sensor mounted next to the plunger coil and it looks like that’s going to work just fine. I’ll find another use for the multi sensor.

Put the relay coil across the bell and not the switch.

There’s no voltage change across the coil either, whether the doorbell is pushed or not, so this won’t work.

Are you measuring this in AC setting on your meter? I would hold the button a little longer just in case the digital meter is slow to react.

Yes, and I had my wife hold the button. 18.5VAC open, 18.5VAC while button held.

Also tested continuity and resistance, no change with button held or open. Makes sense, it’s a copper wire coil, not a resistor or other load.

Which reed sensor did you buy from Amazon? Please post a picture of your setup. I am interested in tackling this as well.

Here’s the reed switch I bought. I’ll grab a pic a little bit later, have to get the ladder out again since the doorbell is about 9 feet above the ground.

I had a friend leave last night and barely tap the doorbell button on his way out, the doorbell rang but the on/off was so quick that the reed switch didn’t pick it up. Have to see if I can remedy that. A solid “normal” press gets it, but I don’t want to miss the quick presses.

Pics. Did some more testing and it picks up all of the normal doorbell presses. If I try to make a super short press by pushing the button and sliding my finger off really fast it’s about 50/50, but I’m having to try to make it a short enough press to do that. Seems good enough for now…if it seems like I’m missing events I’ll switch to the multisensor instead, but I think this will work ok.


Awesome thanks for posting!

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Well my doorbell doesn’t have the coil that I can use a reed switch with. It’s 12v AC and when pressed the voltage goes down from 12 which seems odd. When you let go of the doorbell button the voltage goes back to 12. But at least something changes when the doorbell is pressed.

Anyone have any ideas on how I can connect this to ST so I know when the doorbell is pressed? Is there a voltage sensing relay or switch that will report open/closed that I can hookup an Enerwave relay to?

A relay should work with that. From your description, the relay will be energized/closed when the doorbell is not pressed and open when it is pressed. If you hook up a contract sensor, it will be closed when not pressed and open when pressed. Just make sure you get the proper AC/DC relay, I haven’t heard much of 12VAC stuff before. 12VDC is common automotive stuff.