Self-contained security for memory devices or, alternatively, for other devices and/or other types of machinery to be protected with user authentication. User authentication occurs within the device itself, enabling access to be physically unlocked when the proper security code is provided. A dialing approach is used, whereby a user rotates a disk-shaped device through a sequence of numbers or other symbols, in a similar manner to rotating the dial of a padlock. The device is inserted into a host device or receptacle (such as a Universal Serial Bus, or “USB”, port), and receives power therefrom.