As obesity rises and trousers get shorter, there's been a worrying increase recently in the incidence of Unintentional Bumcrack Display (UBD).
Distinct from the fashion of wearing your trousers round your ankles so everyone can see your underwear, UBD causes inconvenience to those around you, and embarassment to yourself when your slip is pointed out (or often, isn't).
Hence the Moon Unit. The Moon Unit (named changed from Moon Alert in honour of Ms Zappa) looks like those little USB extension spools, but with a tilt sensor built into the spool, and a clip on each end of the 'cable'.
Clip one end to the bottom of your shirt and the other to the top of your trousers (at the back). As long as the top of your shirt hangs below the top of your trousers, the tilt sensor hangs downwards and the device remains silent (and discreetly hidden behind your shirt).
As soon as you sit on a barstool and lean forward (one of the many positions that cause UBD) and your shirt-top rises above the top of your trousers, the tilt sensor flips, and the Moon Unit beeps to let you know of your faux pas before serious trauma occurs.
A more discreet (and possibly pleasurable) option would be a vibrating alert. The precise design is left as an exercise for the reader.-- bumhat, Jan 02 2008 Quality. [+]-- 8th of 7, Jan 02 2008 You could have a solar-powered* alert attached to the inside of the waist of the trousers. If it sees daylight, it lets you know.
*Like you get for calculators that work in artificial light too.-- marklar, Jan 02 2008 //If it sees daylight, it lets you know.//
Except it resides where the Sun don't shine.-- Ling, Jan 02 2008 hm yes, [marklar], that's more elegant, and with no moving parts. It could be like a band-aid - a sticky strip that you attach between the cheeks, with discreet vibrating alert ... I like it !-- bumhat, Jan 03 2008 was with you right up to the "vibrating alert" line. That might cause wearers to want show more crack and we don't need that.-- FlyingToaster, Jan 04 2008 random, halfbakery