I would like to build my own alarm with one arduino and some door contacts .
Door contacts can be hack easily by shunting the 2 wires .
I read some articles where they add 2 resistors.
I thing one resistor is in series with the door contact, the 2nd resistor is in parallel with the 2 first components.
Does someone has already use that kind of circuit?
Can you share some of your experiment?