picture would be nice.
the comm and NC pins are most likely for a SPST relay.
so, you sould be able to put the sensor, facing away from you and then move your hand and hear a click of the relay.
connect your meter for continuity on the outputs.
if it goes between infinity and dead short you know you are seeing it work.
if it is a relay, then just run 5v to the comm and the other pin through a 330 ohm resistor back to a pin on your duino.
if it has power, then use it to power an opto.