Anil Dash’s refactor of Zimeng Xiong’s tinyTouch turns roughly $30 of parts into a fingerprint pad for a Mac that never shipped with one. Be honest about what it is: the device presents itself as a keyboard and types your password for you, so it isn’t Touch ID, it’s a very well-behaved impersonation of your fingers. Your password stays on the Mac, your fingerprint stays on the sensor, and setup runs in a local web page.