Abstract: An electromechanical Smart Lock is unlocked by the Smart Lock timely receiving a time sensitive access-code that solves a cryptographic hash algorithm (e.g., SHA-3 or the like) running on that Smart Lock. To enable this functionality, the Smart Lock knows at least three items of information: status of a countdown timer, its cryptographic hash algorithm, and its unique identifier. Further, the Smart Lock may have various means for receiving the time sensitive access-code, such as, but not limited to, a QR code camera, a barcode scanner, a camera, a microphone, a keypad, and/or optionally, an antenna(s)/radio(s) for RFID/NFC inputs to the Smart Lock. Server(s) may also know the same three items of information for each given Smart Lock; and the Server(s) may provide time sensitive access-codes to (authorized) user(s) and/or to their devices. Users may request, receive, and/or send the time sensitive access-codes via text messaging (or other means).