Need help identifying N.O. or N.C.

["John Brummitt" <jdb5@xxxxxxxxxxxx>]

I'm having trouble figuring out the type of sensors I have ( N.O. or N.C. )
Each zone has a 15K resistor from the loop power to the zone.

The wireless receiver has 2 wires running to it to supply 12 Volts and each
zone has
1 wire running back to the zone screw where the 15K resistor is attached so
that the 15K is always
supplying a little power to the zone screw.
When the zone is tripped the wire from the wireless receiver becomes a
ground for that zone.
So the power flows from the loop power through the resistor, then through
the now grounded wire.

Would this be a N.O. or N.C. circuit?

Thanks,

John
jdb5@xxxxxxxxxxxx