These cufflinks from Adafruit Industries are made of machined aluminum to look like the power button on an Apple computer. Inside the cufflinks are tiny circuit boards and LEDs. Insert a battery in each before wearing, and the power symbol will glow with a pulsing light for 24 hours. The source code, circuit board files, schematics, and CAD files are posted on GitHub, so you can modify them as you like. The iCufflinks are available directly from Adafruit for $128.