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Thread: Strange 4 wire zone for a door

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    Exclamation Strange 4 wire zone for a door

    I've been pulling out an old DSC PC2550 panel and replacing it with a Bosch panel.
    So far so good, I've done the front door reed switch and several PIR sensors and they work fine.

    However the zone which is labelled as 'laundry door' has 4 wires, red/black, white/blue (just like the PIR and window break sensors).
    I was expecting 2 wires for a reed switch, just like the front door.

    Opening the laundry door doesn't trigger the zone.

    This circuit behaves like a powered sensor. When powering red/black I measure the correct EOL resistor value (1k) between white/blue.
    If the power is cut then white/blue goes open circuit as you would expect.

    Why would a door sensor need 4 wires?



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    Is it a detector that is looking at the laundry door or nearby? Can you see an actual switch on the door?

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    to turn on a camera ????

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    Quote Originally Posted by Andrewpv01 View Post
    Is it a detector that is looking at the laundry door or nearby? Can you see an actual switch on the door?
    I cannot see any sensors or wiring near the door, or signs of where a magnet might of been placed.

    I measured the sensor current at 8 mA which coincidentally is within 0.5 mA of the current drawn by each of the window break sensors.
    The PIR sensors I have are each pulling about 17 mA.
    These were probably all installed at the same time about 25 years ago.

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    OK, found it. It was a glass break/vibration sensor fixed to the door frame in between a wooden inner door and outer screen door.

    Not sure what they were trying to achieve with that arrangement.
    Last edited by mb2; 06-03-20 at 04:50 PM.

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