Abstract: A calculator anti-theft system for preventing theft of small, personal electronic calculators comprises a keyboard, a display, a calculator device, and means to store an anti-theft code individual to each calculator. The anti-theft code may be stored within the calculator device or may be stored in an external device. The calculator device is programmed to compare a specified number of the keyboard entries immediately following power-on to the individual stored anti-theft code. If the initial keyboard entries match the anti-theft code, the calculator is enabled, and normal operation is possible. If these first entries do not match the code, the display, the keyboard, or the calculator itself is disabled to prevent normal calculation. In other embodiments, comparison of the stored anti-theft code to the initial keyboard entries is made in a device external to the device which performs the normal calculation functions.