[Jay] hacked a Blu-Ray laser diode into a keychain enclosure. He found a heavy brass keychain light from Lowe’s and stuffed the diode and a larger battery inside. The existing batteries weren’t powerful enough, so he drilled out the endcap to fit a 200mAh 3.6v lithium battery inside. He also modded the power button to only momentarily turn on the diode. With the larger battery, the laser can run for about an hour between charges. In addition to a Blu-Ray lasers, he also has versions with a 200mW red diode.
Related: Laser projector zippo
With a user interface consisting of two buttons and a three digit display, the GPS finder guides the user back to a saved location. Nine locations can be saved for navigation recall. Press a button to save location and press another button to recall. Each switch has a secondary function, for management purposes such as memory indexes and power features. An AarLogic GPS 3A module and AVR microcontroller make up the guts. With the popularity of Geocaching, this would make an impressive trinket; Leading the hunter to an undocumented treasure.
The Coby DP-151sx Digital picture frame keychain seems to be ripe for hacking. At roughly $9, you get a screen, and Li-Ion battery. That’s not bad considering a similar screen alone would cost $20 elsewhere even though it runs on a slower serial connection. While they’ve only put a 3 color pattern on it so far, more can’t be far behind. If you don’t feel like actually tearing it apart, there are some projects that have managed to customize what it displays via the USB connection.