I'm an electronics noob willing to learn. So I have a door bell that looks like it is wired like this:

classic door chime

And I've bought a fancy 3V battery powered device that is intended to be wired simply like this:

fancy door chime

Now I would like to trigger both with the same door bell push. (The push is already in place with wires going where I wouldn't really want to disturb them.)

So how would I go about this?

I know enough that I can't just connect both together. And I've learned that there is a way where a circuit with a transistor can act as a simple SPST switch (see https://www.electronics-tutorials.ws/transistor/tran_4.html, https://www.nutsvolts.com/magazine/article/may2015_Secura, and a number of similar tutorials/descriptions).

But that is how far I got. What would possible approaches to this?


  • \$\begingroup\$ It seems possible the black box does not use logic signals nor can we assume to be ground switch or supply switch. So until you define it, we can only guess. You can measure it though. \$\endgroup\$ Commented May 16, 2020 at 11:28

1 Answer 1


Wire a relay that can be triggered with 6V in parallel to your chime. That relay will look like a closed switch when the coil is energized.

By the way, your 2× 3V battery setup is very strange; since the permutation of devices (switch, batteries, chime) in this setup doesn't matter at all, as long as all stay in the same direction, you'd normally have one set of batteries in one place, rather than distributed to both "sides" of the chime. When you rearrange that, you can see that you can replace your two 3 V voltage sources by a single 6 V voltage source – which, in the case of a door bell, can usually just be a cheap "wall wart" power supply, which will probably be easier than replacing the batteries occasionally.


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