It would appear that the "open_A" point is a pull-down signal for the gate.Your transistor is drawn wrong, it has no collector supply.?
That added transistor circuit I proposed should do that.I want to find solution that openA opens (stay open) if NC contact is NO, or wire to firealarm NC contact is cut.
by Duane Benson
by Jake Hertz
by Duane Benson