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I have brought some Honeywell Actuv PIR (Passive InfraRed) detectors. I know that zone wire contacts become open circuit when it's triggered. How can I detect this using my Arduino?

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    \$\begingroup\$ Same way you would detect any other NC switch. \$\endgroup\$ Oct 20, 2013 at 13:15
  • \$\begingroup\$ The question really has nothing to do with Honeywell or PIR sensors. \$\endgroup\$
    – user30080
    Oct 20, 2013 at 18:32
  • \$\begingroup\$ LOL Sorry I forgot it's just a bloody switch therefore I treat it as just a regular push switch. Dont know why I didn't think of that. Thanks guys. I only said Activ pir just to clarify it's not one of those 3pin pir modules which slightly different. For one they're not pet resistent \$\endgroup\$
    – Ageis
    Oct 20, 2013 at 19:57

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Just treat it as a normal push switch. If there's not already, you'll need to add a pull down resistor, since it's normally closed/ X voltage, but when pushed it is 0 volts, but there will be "static" left in it that your Arduino can't detect. (For a lack of a better explanation; just look up pull up/down resistors if you want to know more.)

WARNING: Nobody else has mentioned this before, so I've taken on the responsibility to do so. Make sure that the switch is operating at less than 5V. (3ish V or above for digital, but you should be able to get away with very little voltage with an analog pin.)

I don't know how isolated the switch is; you'll have to judge how the Arduino will affect the circuit and vice versa. Consider pull up/down resistors like I said. If you don't feel knowledgeable to do this, get advice. It's better to ask advice and wait a day than to not get advice and have no Arduino. (I speak from experience with many gadgets that I tried to rig, yet no Arduinos hurt actually... yet. Haha.)

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