If you need a way to restrict access to power tools to only authorized users, Casey Horton’s magnetic card reader setup, shown in the video below, looks like a great solution. 

When you swipe the correct card through a reader mounted on an 8”x8”x4” electrical enclosure, the Arduino Uno inside turns on power to the equipment via a relay.

The system uses a USB host shield to interface with the reader, and a datalogger shield to handle file manipulation and record who swipes in at what time. Admin mode is accessed by holding the device’s single button by swiping the correct card, at which time another magnetic card can be swiped and added. 

Full instructions and code are available here.