“Enter the code”: The history and design of the most common combination lock in the USSR

In a new article on Habr, the author provides a detailed technical breakdown of one of the most common combination locks installed in Soviet apartment building entrances. The device, which succeeded earlier relay models, became an iconic element of Soviet daily life. The author performs a “nostalgic unboxing” of the unit, examining its internal components and the principles behind its mechanical and electrical circuitry. The article analyzes the design features that allowed this lock to become an industry standard at the time, while also highlighting differences from previous versions. The piece is of interest to enthusiasts of retro technology and the history of engineering, offering a deep dive into the design of simple yet reliable access control systems from the last century. The author demonstrates how the code entry logic was implemented, providing insight into why these devices remained on the doors of millions of Soviet citizens for decades.