Amy Khoshbin made this really funny wearable tech project, the Butt-crack detector:

using a Lilypad Arduino, vibrating motor, and a photoresistor (measures the amount of light in your coin slot), you will make a wearable apparatus. when the photoresistor/your coin slot is covered, the hip-pack is at rest, when it/your coin slot is exposed, this triggers the vibrating motor to start vibrating & let the user know.

Via MAKE.

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LilyPad Arduino