When checking if your flies are done up, there has never been a discrete way to do so.  That is until now, as a trouser hack makes your clothing vibrate when the zip is down, allowing you to subtly check your fly...on the fly!

Instructables Technology Editor, Randy Sarafan, explains the technology making this a reality.  Using conductive thread, a small circuit board, and a vibrating motor, he's managed to solve this ever-present problem of indecent exposure.  

Tap a button in your pocket, and the Discreet Pants Fly Checker will vibrate if you're all zipped up, or not, giving you an opportunity to slip away and zip up the fly.

Possibly the single greatest answer to a question that people never knew they were asking.  Good luck getting through airport security with this though..