Call A Cell Phone, Find A Tent

relay Finding your tent at a music festival is a tricky endeavor – not only are there miles and miles of tents exactly like yours, you most likely have a few beers or other substances in you that affect your sense of space and/or time.  [James] came up with a great solution to finding your tent by illuminating it with Christmas lights and a cell phone.

The basic idea of [James]‘ build is having Christmas light flicker whenever he calls a phone. One feature in nearly every phone that can be exploited to accomplish this task is the backlight turning on when a call is received. Add a phototransistor, a little bit of circuitry, and some Christmas lights, and you have a fully functioning tent finder.

[James]‘ circuit is a simple relay driving the Christmas lights, triggered by a phone right on top of the phototransistor. It’s a simple circuit that can be built on a piece of veroboard, and with a few pieces of plastic forming the enclosure, provides a reasonably bulletproof device that will survive the rigors of a music festival. As a bonus, there’s no need to modify the phone to trigger a remote circuit. Video of the device in action below.


  1. hfiennes2 says:
  2. ianmcmill says:

    Either the circuit lights up the tent or the circuit lights up the tent. I prefer the first possibility.

  3. r4k says:

    Pfft. People have been using GPS to find their camps at BurningMan for nearly a decade now, and that’s only because strobes held aloft by helium weather balloons don’t cut it any more.

  4. notabena4us says:

    +1… Great idea!!!

    Can also use it to modify your running Daylight Headlights to switch off or run 6000K LEDS for Daylight Running Lights too!

  5. Yolty says:

    It would be easier and possibly cheaper to do with a 2-way radio.

  6. rockdots says:

    In my experience, getting cell phone coverage at festivals is harder than finding my tent… usually the local cellular tower is overloaded with the crowds…

  7. catinthebobs says:

    Am I the only one here, who thought that this is perfect for a bomb?
    Even the word “trigger” gets used over and over in the article…

    just sayan

  8. Hirudinea says:

    “Dude, I lost my phone, can you call my tent?”

  9. Jme says:

    Never have mobile reception at festivals I’ve been too. A big flag on a gigantic pole is always enough

  10. justice099 says:

    How about a “find my car” app on the phone? I actually use this quite often, not just for locating my car.

  11. ddsouza says:

    “google now” already has a feature to find where you parked. using the gps i assume, you could make a similar app to find your tent and/or track your route from tent to other places. or use a gps.

  12. Anon says:

    Or, how to make an IED….

  13. John says:

    I Agree, you realize that these people are publishing plans for a mobile phone triggered detonator.

    The standard nokia comes direct from the manufacture already equipped with timer, Emergency override, manual detonation, GPS location etc.

  14. HC says:

    Can we start some kind of petition for Hackaday to stop covering hacks that make something more difficult than it was before? If you have a smartphone, you have a GPS receiver. If you don’t, you can pick up an old handheld GPS unit for ten dollars on ebay, which is a hell of a lot cheaper and less hassle than getting an old phone, getting service for it, and building this contraption, to say nothing of the likelihood of you not getting any kind of cell reception/service at the festival location.

    Yes, you COULD set up a kinect mounted to a set of peepholes in your front door so only someone who knows the secret dance can get in, but you shouldn’t, because it’s fucking stupid.

  15. james says:

    except your phone dies at the festivals.. and do you have to leave your phone in your tent?? that sounds silly. :)

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