When I first tried hooking this up to my Arduino I was worried about the sensor running on 12v. I didn't want to pass that voltage into the Arduino and fry it. Eventually I realized that the signal pins are left floating when the alarm is not triggered. When the alarm is triggered the signal pin is connected to ground. This means you can connect the signal pin to a Arduino digital input pin, but you need to connect it to a pull up resistor so you get a constant value.