Hacking my home alarm

[Sander Stolk]

What I would like to know is the following:

I have a alarm system in my home which has a connection on the backside for a dialer-module.
This connection has 3 screws: + , - and Dailer.
When I measure the voltage from + and - I get an 12v.
When I measure the voltage from - and dailer I get an 0.01v on my multimeter.
When I check if - and dailer are linked the beeper in my multimeter goes on and I get a value of 35 Ohm.

Long story short: When the alarm sounds the - and the dailer are disconnected hence a Normally Closed connection.

Can I just connect those - and dailer to a digital and GND pin on a Arduino Nano?
Or do I have to have a resistor between this Digital pin / GND connection?

[TheoL]

@Sander-Stolk I would never add any device directly to my Arduino. Can never do any harm to put an opto-copler in between. If you're lucky the only thing that gets damaged is the arduino.

But that's just my 50 cents.

[Sander Stolk]

@TheoL Well I tried with an opto-coupler but I just didn't got it worked from the output for a siren.
So I found this Normally Closed connection and this is an easier way for me to use a a button. I get the point that some equipment can break or damage something but on the other side if it's broken it's only going to cost me some $ for an new Arduino and a NRF24 module. No other equipment is connected to this Arduino sensor.

[TheoL]

@Sander-Stolk I'm guessing your Home Alarm must be protected against over power and thinks like that. It's worth the risk. Maybe you can connect a good old transistor? Just to separate the circuits.

I'm by far no expert. But I just don't trust the 0.01V that's a low and strange value. At least to me it is