The purpose of this design is to emulate as closely and as simply as possible the traditional rotary combination lock. Full emulation would be possible with a complex design - close emulation is possible with a remarkably simple circuit - in this case using just two CMOS i.c.s and three transistors.

Pseudo-rotary combination locks are well known. These usually use a combined dial and pushbutton, with limited rotation of the dial. The dial is usually turned to a number in the sequence, then a pushbutton is pressed to register the number. Both this and the characteristics of the standard wafer rotary switch (its rotation-limit-stop and snap-action) make such locks seem poor substitutes for the real thing.

This design has smooth 360° rotation, does not use a pushbutton switch, and offers roughly twice the security of a 4-digit keypad lock. It also prevents aimless turning of the dial, and is able to send a secret panic (duress) signal to another location. The last two features are optional, and may be built onto an additional printed circuit board, which may also be interfaced to a standard intruder alarm system.