Transform a Wired/Powered Doorbell into Smart-ONLY Device?

(Rich Heimlich) #1

Okay, so sometime ago I changed my wired doorbell into a semi-smart device with a dry contact sensor and a reed switch (thanks Community).

Now that Alexa can be controlled to play files and speak via software, I’d like to revisit this and understand what I would need to completely remove the physical doorbell from the equation.

I’d like to power a wireless device by taking the power from the doorbell now and drive a sensor of some sort (can I just use the dry contact sensor?) by connecting the two wires from the ringer button right to that.

Would that do it?

I know I’d need a voltage adapter to convert the voltage over to whatever the smart sensor needs. Does anyone know what voltage is provided to standard doorbells? 12v?

Once that’s done I can clean up the wall and perhaps just leave a SMALL hole for the wiring to get to the sensor and then the only thing you’ll see is the sensor. No more large bell box.

(Robin) #2

The dry contact sensor needs a dry contact, so yes, you would just connect the two terminals of the push button directly to the two terminals of the dry contact sensor. Do not apply a power supply to the dry contacts of the sensor.

Doorbells vary in voltage, so you will need to check the spec which should be stamped on the doorbell transformer, wherever that is positioned (normally next to the consumer unit).

(Rich Heimlich) #3

Thanks Robin. It sounds like I can eliminate the physical doorbell now then and work on the powering of the battery jack of the sensor as a second step.

Much appreciated.

(Robin) #4

I personally I would keep both… that way if the internet, ST or Amazon clouds are down you still know someone is at the door via an old fashioned ding dong.


It’s exactly the same approach as the pressure Mat, you’re just using a button instead of the mat.

(Rich Heimlich) #6

You make a good point.

(HousePanel Author) #7

Damn … this is brilliant. I can just hook up a window sensor to my doorbell contacts and be notified when someone rings the doorbelll regardless of where I am. I wish I had thought of that before I bought a ring doorbell but then again it is a nice product.

(Robin) #8

Not exactly… your existing doorbell has a power supply, which passes through the push button and onto the bell (wet contact)… if you hook up a dry contact sensor to that it will blow.

You could use the button and sensor on their own but you’d loose the bell / have to rely on the internet to ring a smart siren.

To use a dry contact sensor alongside an existing bell you will need a cheap (dumb) relay to seperate the voltage from the sensor. Wire the coil side of the relay in parallel with the bell, and the switched side of the relay to the contact sensor.

(HousePanel Author) #9

Yup - I get it. I used a simple $4 relay to set up my garage opener using the same concept back in the day before integrated Zwave openers were available.

(Rich Heimlich) #10

Slightly confused. Didn’t you say above that, “you would just connect the two terminals of the push button directly to the two terminals of the dry sensor contact”? I was under the impression that power to the two wires heading to the button was supplied by the transformer at the physical door bell unit in the house. The only reason I want to involve power is to step it down and use it to power the sensor itself.

I did speak with the wife and the Internet here goes out so rarely that losing the doorbell then would be very minor. The doorbell is out anyway when the power is out so that would remain the same. We’d gain a lot of options on flexibility of tunes and such. I’m even thinking holiday-based rings and such. That’s hard to pass up.

(Robin) #11

Yep, but that is for a solely smart option, taking the doorbell and transformer out of the equation completely.

The point is, a standard door bell system has voltage running through it, supplied from the bell unit or a transformer, wired in series with the circuit.

A dry contact sensor supplies voltage to run through the switch, from its internal battery… apply an external voltage through the contacts of a dry contact sensor and it will go pop!

(Robin) #12

As this question gets bounced around a lot… I decided to knock up some schematics to better describe the options available:

NEW: Fibaro Door & Window Sensor 2
(Rich Heimlich) #13

Thanks. Much appreciated!