Discreet Pants Fly Checker




About: My name is Randy and I am a Community Manager in these here parts. In a previous life I had founded and run the Instructables Design Studio (RIP) @ Autodesk's Pier 9 Technology Center. I'm also the author ...

People are always wondering how it is that I make so many inventive things. This is normal day-to-day stuff for me. I just do it. I don't really know how to do anything else. What is more mind-boggling to me is how everyone else does those other things like clean their homes, feed themselves, and get dressed in the morning. These commonplace tasks that people take for granted I find utterly challenging. While there are so many things that I struggle with, one such task I'm particularly bad with is remembering to zip my fly back up after going to the bathroom.

The Discreet Pants Fly Checker was made with this in mind. Basically, this is a device that lets you discreetly check in public whether or not your pants fly is up. By pressing a button located in the watch pocket of your pants, a small pager motor alerts you to whether or not the zipper is up. Basically, the zipper of the pants was enhanced with two strands of conductive thread which  form a complete circuit when bridged. A small circuit board with a battery, button and motor attached then snaps into the watch pocket. Finally, when the button is pressed, and the zipper is closed, the circuit is completed and the motor vibrates.

How discreet you want to be about pulling your fly back up when it is down is up to you, but at least you do not have to be grabbing your crotch uncertainly all the time. That at least is a drastic improvement.

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Step 1: Go Get Stuff

You will need:

(x1) CR2302 battery holder (Radioshack #270-009)
(x1) CR2302 battery (Radioshack #23-802)
(x1) Vibrating pager motor (Radioshack #273-107)
(x1) Tactile switch (Radioshack #275-002)
(x1) 1.75" round PCB (Radioshack #276-004)
(x1) Round tube pen
(x1) Spool of conductive thread
(x1) Pants with watch pocket
(x2) Sewable snaps

Step 2: Battery Holder

Solder the battery holder to the 1.75" round PCB, such that the holder itself is on the same side as the copper solder pads.

It may be helpful to tin (apply a small amount of solder to) the pads that you intend to solder to ahead of time.

Note: the attached circuit diagram applies to the next 10 steps.

Step 3: Button

Solder the tactile button swithc to the (designated) top side of the 1.75" round PCB

Step 4: First Snap

Strip the insulation off about 3" of solid core wire.

Pass it through two holes in the circuit from the copper side on through to the back.

Slide the button snap onto these wires so that it lies flat on the backside of the circuit board.

Bend the wires over and pass them through the other mounting holes on the button snap, and then back through the board.

Pull the wire taught.

Solder the wire to both the copper pads and button snap.

Trim away any excess wire.

Step 5: Ground It

Solder the first snap attached to the ground terminal on the battery holder.

Step 6: Second Snap

Attach the other snap in a similar manner to the other edge of the circuit board such that they are about 1.25" apart.

Step 7: Solder

Connect the second snap to one of the terminals on the tactile switch.

Step 8: Trim

Take apart a pen tube and cut a section that is slightly larger than your vibrating motor.

Step 9: Insert

Insert the motor into the pen tube.

Step 10: Glue

Glue the motor into the pen tube while making sure the motor can stil spin.

Once that is dry, then glue the pen tube to the circuit board.

Step 11: Solder the Motor

Solder the motor's ground lead to the switch terminal opposite to the terminal connected to the snap.

Solder the motor's power terminal to the positive terminal on the battery holder.

Step 12: Insert

Insert the battery with the '+' side facing up.

Step 13: First Thread

Cut 3' of conductive thread and fold it over onto itself. Pass the creased end of the thread through the eye of the needle to quadruple the number of threads. Tie the thread ends together with a knot.

Starting from the top, count down six pairs of zipper teeth, and make a stitch in the center of this pair.

With the same length of thread continue stitching between every other set of teeth until you reach the top.

Once at the top, using a running stitch, sew along the pants seam until the thread is over the watch pocket, and then sew down into the pocket.

Leave the thread attached to the needle for sewing the snap base on.

Step 14: Second Thread

Thread another needle with quadruple strands.

Stitch between the opposite set of zipper teeth, while being very carefully to keep the threads from touching or overlapping. If the threads do get close, they can later be tacked apart using a non-conductive thread preferably matching the color of the pants.

Make another conductive thread trace following the seam, and again not touching the other trace.

Finally, stitch this thread down into the watch pocket, also leaving the needle connected.

Step 15: Finish Snaps

Sew the based of the snaps into the watch pocket approximately 1.25" apart.

Step 16: Connect

Insert the circuit board into the watch pocket and snap it into place.

Step 17: Use

Whenever you want to check if your fly is down, simply press the tactile switch. If it does not vibrate, find a discreet place to go to pull your fly back up.

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    71 Discussions


    1 year ago

    Would be super cool if you could wire it to zip it up for you after finding out it was down. Maybe a next project for you? But awesome nonetheless ;)

    1 reply

    Reply 1 year ago

    That's an idea. I imagine that the mechanism needed to return the zipper to its original position would require a lot of force. I will think this one through! :)


    2 years ago

    I like it! Very wear-able!


    5 years ago

    I agree with Chopper Rob (Jul 30, 2013) :)


    6 years ago on Introduction

    I had the same problem with a favourite pair of jeans, the zip would work its way down. My solution was to put a 1" split key ring through the hole in the zip pull toggle, which both helps pull up the zip by hooking in my index finger, and the ring is then hooked over the copper button before putting through the button hole. The fly can't open without undoing the top of the jeans first (a sort of chastity belt mod as well).

    3 replies

    Reply 6 years ago on Introduction

    Low tech is best, KISS, Keep It Simple Stupid.
    One could just attach a spring to it so it zips itself up.
    Just keep a good grip on it while taking care of business.


    6 years ago on Introduction

    Wonderful! This is almost the ultimate in wearable technology! For those - like me - who do not remember to "discreetly check", how about tweaking your invention to send a text message to the wearer if the zipper remains down more than a few minutes?


    6 years ago on Introduction

    Cool. When I saw the first picture, I though the round PCB was a photocell, and I go to myself, "This guy has a photocell behind his fly to check if light will get through?

    Good thing that wasn't it.


    6 years ago on Introduction

    This is without question the single most practical e-textiles project I have ever seen.


    6 years ago on Introduction

    Well thought out. Especially with snaps. Nice presentation. Now replace the switch with an LM555, 2 resistors and a capacitor and have it check every 30 seconds for you!
    see http://home.cogeco.ca/~rpaisley4/LM555.html

    1 reply

    Reply 6 years ago on Introduction

    Pretty awesome idea but then you'll start getting ghost vibrations like your phone provide ;)


    6 years ago on Introduction

    This is a fun project and I am tempted to try it but it falls into the Rube Goldberg approach to doing things. A very simple fly checker is either your eyes or your hands. No batteries required.

    2 replies

    Reply 6 years ago on Introduction

    Ya I had high praise for the effort, buuuuuuut "Rube Goldberg" did flash to mind, and how about using,Arduino, or a pc with quad core CPU 16 gig ram an bluetooth to and nex gen robotics to keep your violin case shut........ or maybe just a pair of button fly LEE's... but whats the fun in that :)


    Reply 6 years ago on Introduction

    unless you suffer social anxiety which basically results in paralysis - you're afraid your zipper is down, but if someone sees you checking they might think you're a pervert. the resulting situation is the donkey dilemma (positioned exactly equal between two bales of hay, the donkey was unable to make a decision and starved to death).


    6 years ago on Introduction

    An interesting idea but, like Winston Churchill, I don't have to worry about a dead bird falling out of the nest.


    6 years ago on Introduction

    Great idea, made me laugh a bit because of this simple ingenuity. On the other hand, I'd have rigged the thing so that it vibrates when the fly is down only, such as if you press the button on accident, or you've got something compressing your pocket (may it be your little nephew on your lap or rush hour in the metro) it doesn't buzz incomfortably.