Using existing security door sensor as a trigger


I am going to start building this little project I have been wanting to do for a long time. I am wanting to build a door chime that goes off as the door is opened. I will be installing it in my business that has an existing door sensor for a security system that is still in use. The system uses 13v DC as the current sent out to all sensors. Its just a standard reed switch on the door.

My idea was to see if I could just splice into the existing sensors wiring and run it to the Arduino to trigger the mp3 or whatever music file I choose to play using the Adafruit Music Maker Shield. Obviously the Arduino would need to not interfere with the voltage going to or from the reed switch, only activate the tone once the voltage is either applied or taken away. I haven't figured out yet if the voltage is always on and off when the door is open or always off and on when the door is open. But either way should be simple to program I would think.

I know the alarm company probably wouldn't approve but if this works how I think it will they will never even know.

Is this possible with the arduino?

I would be wary of tampering with the security system. If the door has a magnet that triggers an existing reed switch why not install a second separate reed switch for your Arduino project?


Exactly. Especially if it is managed system, don't touch. Anyway, you may find that the door contacts are not a simple read switch construction. These sometimes have resistors built in so the control unit can detect open and short circuits. The easiest, non intrusive solution would probably to use a cheap passive infra red sensor for your chime.

This is an easy project for a beginner but as others have said, it's best to leave the existing 'read switch' alone and just install another alongside for your bespoke project. They are very cheap, just two wires on the switch and a magnet. Far better than fritzing your alarm!

Detecting a door switch to play music on an MP3 player is straightforward but requires a bit of Arduino knowledge, such as using the I2C bus (easy - two wires plus power). I recommend you start by detecting the door switch and then beeping a sounder (or buzzer) or just lighting an LED to prove the concept, before using an MP3 player.

What you really *need is someone who has done all this before and who could show you how. **Wow!* What a coincidence! My YouTube channel now has over 50+ videos designed for just an occasion, including how to use an MP3 player (see Video #34, MP3 player may be the same as yours, but should give you ideas anyway).

URL is in the footer of this post, have a look, it may help you move your project forward. :)