Smart Pants Sound Alarm When Your Fly Is Undone

It’s always embarrassing to be told your fly is down. Even moreso when you realize it’s been that way since you returned from the bathroom an hour ago. [Guy Dupont] has built a device to solve this awkward issue once and for all. (Nitter)

Pictured: The Hall effect sensor and magnet attached to the zipper.

The pants contain a Hall effect sensor which has been attached inside the fly of the jeans, at the bottom of the zipper. The zipper pull itself was then fitted with a strong magnet, which triggers the sensor when the zipper is in the open position. An ESP32 in the pocket of the jeans is tasked with monitoring the sensor. If it detects that the zipper has been down for too long, it sends a notification to the wearer’s smartphone to zip up. We kind of wish they’d sound an ear-splitting klaxon, but that might draw undesired attention to the wearer.

Zipper position monitoring seems like a nightmare at first, but [Guy]’s hack shows us that it’s actually trivial with this method. The system does, however, add significant complication to what was previously a totally-analog pair of pants. Don’t expect “Big Jeans” to jump on this tech, as maintenance and waterproofing issues would likely make the hardware a pain to deal with in real life.

Plus, just imagine the frustration every morning. “Sorry, mate, not ready to head out yet – I’ve gotta pair my jeans with my smartphone.”

27 thoughts on “Smart Pants Sound Alarm When Your Fly Is Undone

    1. The logic fail on this project is easily fixed. Rather then telling you your fly is down; you are really interested in making sure it is up!

      If you are verifying it is closed, then a missing magnet or failed sensor would more likely generate a false report of an open fly. Whereas this arrangement does not even accommodate a half open zipper, still would read as A OK.

      Put sensor at top, then it will check that it is up!

  1. Big jeans would jump on this. They could encapsulate the whole thing in epoxy to waterproof it. As a bonus you don’t need to charge the battery – one CR2032 cell should last longer than the knees on most pairs of jeans… 😭

  2. : ) This project is small enough that I’ll just document it right here:
    – sensor is a Honeywell SS441R (hall effect sensor with digital output, works at 3v!)
    – Chopped the end off a Stemma/QT cable, soldered power/gnd/data to the sensor.
    – Hot-glued the leads for protection, also hot-glued in some safety pins to attach to pants.
    – ran cable through small hole in inside of front pocket, hook up to Stemma/QT port on Unexpected Maker FeatherS3
    – Feather is running on a 400ma lipo, running CircuitPython
    – Feather sleeps until sensor pulls its pin low, immediately tries to connect to WiFi upon waking. Once connected, checks that the sensor output is still low for a few seconds then makes a POST request to my Pushover account, which sends a native Android push notif to my phone.
    – Wait 30ish seconds to “debounce”, then back to sleep.

  3. In addition to the klaxon, there needs to be flashing lights and perhaps one of those “merge now” illuminated arrow sign things that alert others not to look at the potentially offending gap…

    Or a little flag that pops out and exclaims “DON’T LOOK AT THIS!!!”

  4. It needs the Back To The Future touch as in the voice ” Your jacket is drying… Your jacket is now dry..”.. something like ” Your pants are unzipped… Your pants are now zipped”. However it could be painful if it jumps your gun…

  5. I see two problems:
    1) Might not detect a partially open condition
    2) Magnet might interact with the environment in unwanted ways
    It seems better to have the detector at the top to solve problem one. For problem two, instead of an expensive hall sensor and extensive modifications, perhaps simply soldering wires to two adjacent teeth near the top of the zipper would allow them to serve as switch contacts. Contact bounce would likely be a bit of an issue, but not difficult to work around.

    1. Both excellent ideas, and I originally intended to put the sensor at the top! Was limited by cable length and did not want to make a new one last night.

      And I also like idea two, though I have a hunch it’s gonna be difficult to solder well enough to get a solid mechanical connection without getting in the way of the actual zipper. For me, at least!

      1. Maybe the teeth could be machined to provide a better mechanical joint, such as a groove for the wire to sit in. Something like the solder cup dsub connector pins.
        Other than that, just use plenty of flux, a hot iron with plenty of thermal mass, a pre-tinned wire, and a quick in-and-out motion to prevent scorching the fabric. In fact, wetting the cloth first would probably be advisable, but watch out for steam!
        (Full disclosure: I’ve never soldered to a zipper before.)

        1. Too complicated. Requires wire to run around the zipper to make circuit.

          Magnetize zip. Detect it’s at the top. Homebrew: replace zipper handle with magnetic one if zip is non ferrous.

          Keep the circuit entirely on one side. Near the top where the fabric is already 4 layers thick, but below the belt.

          You could tazer the user in the balls if it stays unzipped too long. Sell device to ‘sit to pee’ (British term of affection for mates, rhymes with punt) to use on their simps. Tricky to get fastened. Got to be fast. I digress into marketing.

          Probably better just to play a stream running sound when the zips down. Dual function for shy bladder types. Also Japanese toilet weirdness. Good market for gadgets.

          You’ve got to find a zero effort way to disable the alarm when pants are off. To avoid playing ‘find the alarm pants’ in the hamper at 6 am (when on the ragged triple point between passed out, still very drunk and hungover).
          Or other scenarios, don’t want cock blocking pants. Loud alarm going off right next to GFs ear (just have it play ‘lets get drunk and screw’).

          If the sound it played was hackable there would be lots of fun to be had. At the wearers expense. Rick rolling would just be the beginning. Your buddy has an assignation (froggish for ‘booty call’) this evening. You know how to remotely update zipper down noise. What to do, what to do…

          Better yet, in bar full of yuppy scum. Update them all.
          Write a zipper rickroll virus that propagates around the world.

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