Techniques are disclosed relating to securing physical compartments and allowing users access via a mobile device configured to use a mobile authentication system. In some embodiments, a locking device for a physical container is configured to unlock only if both a transaction authentication system confirms successful authentication of a mobile device and an auxiliary key is present. The locking device may receive encrypted data from the mobile device via a short-range wireless connection, transmit the data to the transaction authentication system, and receive a message indicating whether authentication was successful. The mobile device may encrypt the data using a replenishment key from the transaction authentication system; therefore the authentication may decrypt the received encrypted data to confirm an identity of the mobile device. In some embodiments, disclosed techniques may allow users to use their mobile device to unlock a safety deposit box without requiring extensive infrastructure investment, e.g., because the existing authentication network may be utilized.