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Are zombies trying to steal your yo-yo? Or do you want to booby trap the neighbor kid with a motion-sensing alarm? The PIR Sensor Arduino Alarm is great for both! Combining technologies we’ve used in previous Weekend Projects, this build is entirely solderless. It uses very few components, so it’s a great project for makers looking to get started with Arduino, or who want a quick lesson in digital I/O. The software program is provided, and many of you may already have these components laying around, but never thought to combine them together into an alarm.

If you build this project into an enclosure box of your own design, or come up with a clever use of spooking your friends with the alarm, be sure to send us an email with some actions shots or video, and a story about your build!

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Nick Normal

I’m an artist & maker. A lifelong biblioholic, and advocate for all-things geekathon. Home is Long Island City, Queens, which I consider the greatest place on Earth. 5-year former Resident of Flux Factory, co-organizer for World Maker Faire (NYC), and blogger all over the net. Howdy!



  1. beardy241 says:

    All good and groovy — that is apart from the expensive PIR sensor c. $10

    I’ve created a similar project using two Light Dependent Resistors (LDR) as a voltage divider. When the visible (and IR) light level changes in front of either LDR the alarm is tripped. Two LDRs are MUCH cheaper than a PIR sensor!

    A big plus is that PIR sensors don’t work through a window whereas LDRs using visible light obviously do.

    Best of all, the whole project was ported to an ATtiny85 chip and ran very happily off a pair of AA cells.

    1. Nick Normal says:

      Agree about the cost, but generally I’ve found that a lot of makers already have this specific sensor module. Up front for example the cost of an Arduino is high, but then over time I seem to have two, three, extras always on hand for projects :)

      1. Fry Formal says:

        To those of you who are concerned about cost, have you heard of the smARtDUINO project on Kickstarter? They’re looking to break the barriers down in the Arduino world, making more specific & cheaper components that do all the same things as Arduino.

        1. beardy241 says:

          Thanks Fry, I’ll check that out.

          Apologies if I sounds ranty earlier.

          I agree, Nick, about collecting Arduinos and bits along the way, which is great for experimenting. Permanent deployment however usually means embedding a whole Arduino along with whatever sensors.

          My motion sensing intruder alarm was a project for a dozen kids so embedding Arduinos and PIRs was out of the question. That’s where the LDRs and ATtiny85 came in. The tiny85 costs about $1. I am SO hooked on the tiny85s because they enable so many projects to be released into the wild whereas previously they would have only been neat breadboard experiments. Respect to the MIT team for enabling that transition!

          1. Nick Normal says:

            Didn’t sound ranty at all! We’re just getting people started (and hopefully hooked!) on beginner-friendly projects. Hopefully from here they dive into “projects to be released into the wild” as you say!

    2. SenCan says:

      Sounds interesting. Can you provide a schematic and also arduino program? Thanks.

  2. beardy241 says:

    It might also be worth commenting that Zombies, being cold-blooded, may not trip a PIR sensor when in a large open space because there won’t be any IR difference between them and the distant background. In a confined space it may work ok but you’ll not need warning if they’re right on top of you!

    1. Nick Normal says:

      The fresnel lens operates one way, but a shield or ‘barn doors’ of some sort could also be used to direct the sensor in a specific field. I’d personally bank on being as far away from any large open spaces during any zombiepocalypse – I’d rather be holed up, and have a few choke points to bottleneck and booby trap them!

  3. ~Madlibs says:

    Once everyone is done raiding the guns n food from Walmart I’m going straight for the RC cars and noise making greeting cards. Not the yo-yos

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  7. lol says:

    Face palm….
    You need to add a 200 ohm resister onto one leg of that LED to limit current flow.

    Otherwise you can damage the LED and or the chip on the UNO.

    1. Greg says:

      …Unless you’re using pin 13 which already has a resistor.

      Correct me if I’m wrong.

      1. Nick Normal says:

        You are correct – see my reply to “lol”

    2. Nick Normal says:

      Greg is correct. Pin 13 is declared in digitalWrite to HIGH which enables the internal 20K pullup resistor, per the Arduino reference page:

      “lol” please use your name or email so we can have a conversation in the future kthxbai

  8. [...] Build a Basic Infrared Motion Alarm with Weekend Projects | Make [...]

  9. [...] Build a Basic Infrared Motion Alarm with Weekend Projects | Make [...]

  10. Bosstiger says:

    Reblogged this on Gigable – Tech Blog.

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