Arduino security with frickin’ laser

[over9k] used his Arduino to set up a laser trip wire. The laser is mounted along side the Arduino, reflects off of a mirror, and shines on a photoresistor that interfaces via a voltage divider. The signal from the voltage divider is monitored for a change when the laser beam is broken. [over9k] set things up so that a webcam snaps a picture of the intruder and Twitters the event for easy notification. Video after the break walks through each of these steps.

This build is a bit rough around the edges but unlike other laser trip wires this keeps all the electronics in one place. The laser interface could be a bit more eloquent, and we’re wondering just how much current it is pulling off of the Arduino pins. But if you’re bored and have this stuff on hand it will be fun to play around with it.


  1. Gregg says:

    how did you program the webcam to take the picture with a serial command? I was trying to figure this out but had no luck

  2. Nemo says:

    @Gregg-Take a look at the example Arduino program in examples>communication>graph. Inside there is a commented-out chunk that explains serial communication with an Arduino using Processing. Try and combine that with the image capture example from Processing, it should be trivial to get what you want out of that.

  3. Paul Potter says:

    That is a great idea.

    Also, bonus points for using the old cassette box. :)

  4. therian says:

    Laser will not live long in such constant configuration, and dont try to blink it, it will kill laser even faster, what you can do is change current, high, low, high, low but not completely off, diodes doesn’t like that

    another project arduino is not needed.

  5. Reikaze says:

    It’s compact, and it’s a good idea, overexpensive? maybe…

    But it’s not a bad project.

    I like it =D. Just a little delay, a link to a twitpic, and an infrarred laser, will make it for me a must-try.

  6. nave.notnilc says:

    how about a pulsed IR LED + receiver, longer-lasting and invisible.

  7. nitpicker says:

    Eloquent?!? Your English is appalling.

  8. urlax says:

    So this device has a whopping 1(!) digital input which is monitored, and then the PC handles the rest? if you want it quick and dirty, abuse the LPT port for it.
    using a $30 Arduino board for this is such overkill..

    I don’t even care how you do it, you might even use the PWR button on the MOBO and the ACPI deamon.. _that_ would be an hack!

  9. Hitek146 says:

    ^Yea, LPT port…

    LPT ports rare? $4 USB joystick provides PC with four analog inputs and 16 digital inputs, and requires no coding…

  10. Don says:

    I love it. What is a CASSETTE? A small case? Yup It seem like eons ago. Do they still put casettes in boomboxes? Do they still make boomboxes? I miss my AM radio. What was the subject again?

  11. Steve says:

    Eloquent? I think you meant to say ‘elegant’.

  12. Mickey says:

    There is a site that do exactly the same just without any electronics:
    the web cam as motion detection tool

  13. poot says:

    “Hack A Day” should be renamed “Arduino A Day”

  14. Kay says:

    how can i get that kid, from where can i buy it

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