Introduction: Digital access can reduce key waste by replacing duplicated keys, rekeying cycles, and repeated handovers with managed entry.   Residential security is often discussed as a matter of locks, keys, and alarms. Yet the everyday waste behind physical access is easier to overlook: duplicate keys, lost-key replacement, lock cylinder changes, discarded cards, emergency handovers, and repeated service visits. Each event looks small, but in apartments, shared homes, short-term rentals, and family households, the pattern can become a steady flow of materials, travel, and administrative effort. Digital access does not make a home automatically sustainable. A smart lock still uses electronics, batteries, packaging, and installation labor. The stronger environmental argument is narrower and more practical: when a lock can manage access through biometrics, temporary passwords, app authorization, logs, and visual intercom functions, it can reduce the waste created by physical key...