# How do I monitor voltage on a circuit even when switched off?

Here's the situation: I have a baby. Soon, I'll have two. So I don't really like spending half an hour trying to get him to sleep and then somebody rings the doorbell, waking him up.

I've already installed a switch on the doorbell circuit which disables it. I'd still like to know if somebody is trying to ring it though. For simplicity sake, lets say it's a simple light bulb that I'm always looking at, so it doesn't need to stay on. (Just a momentary flash will do).

The diagram on the right is the simple doorbell circuit. On the left, I have my indicator circuit with the 12v relay I assume I'm going to be needing. I believe the relay coil needs to go in parallel with my switch, but I'm not sure if this will work. Do I need a resister between the two?

What am I missing to complete this solution?

****EDIT:** Maybe I did myself a disservice by oversimplifying. The indicator isn't a lamp, it's actually my alarm panel which can monitor for either an open or closed circuit (but not a good idea to put the actual bell on that same circuit). This will allow me to be notified of a doorbell signal by email/text message, or whatever method I choose, even if I'm away from home.

Additionally, I have a dog that barks regardless of whether the doorbell is disabled or not. This is probably outside the scope of the question, however.

• Don't disable the doorbell. Put the lamp in place of the ringer. – R Drast Oct 18 '17 at 12:53

The simplest solution is to teach babies to just sleep in a noisy environment. That might be easier said than done though.

As an alternative you could make this which saves some components.

simulate this circuit – Schematic created using CircuitLab

Note that the indicator lamp should not use too much power as it adds to the power needed by the bell. I would suggest using one or more 12 V LED lights, the ones that replace 12 V halogen lamps for example. These are low power and very bright.

• Our doorbell is very loud, and since we have kids, it woke them up maybe three times or so... – PlasmaHH Oct 18 '17 at 13:14
• @PlasmaHH You mean, they got used to it? I placed a "no salespeople" sign, that also helped. – Bimpelrekkie Oct 18 '17 at 13:16
• Luckily I have never had once in my life any salespeople ring at my door. For the kids, when they sleep they are usually that much tired for being able to sleep that you could set off nukes and they wouldn't wake up. All the times where this happened was in the morning, where everyone was still sleeping. – PlasmaHH Oct 18 '17 at 13:18
• Thank you for the response @Bimpelrekkie. it helps, but doesn't exactly suit my needs, and that's my fault for trying to simplify the question. – Brad Parker Oct 18 '17 at 14:39
• OK, then just replace the indicator lamp with the coil of a 12V relay as in your 2nd schematic, left part. – Bimpelrekkie Oct 18 '17 at 14:43