Fuelbox MP3 is a mini MP3 boombox that is seamlessly hidden in the original Nike+ Fuelband SE package. It is an influencer kit that plays a piece of custom sound effect when the package is opened. Fuelbox MP3 is open source hardware based on Arduino Pro Mini, TI TPA2005D1 amplifier, and $5 MP3 player off eBay. The trick is that a normally closed reed switch is located at the lower-right corner, which is made open by a piece of magnet on the opposite side when the package is closed. Upon opening the package, the normally closed reed switch on longer has magnetic field around, hence it closes the circuit.

Source

Github

Photos