Techniques are described for keyless entry to a structure (e.g., hotel room) utilizing a set-back box. Registrants (e.g., hotel guest) may scan a barcode from their mobile device to check-in to the structure. Upon scanning the barcode or by other means, a mobile device identifier (e.g., a Bluetooth low-energy address (BLE)) is registered and associated with the checked-in structure. Receiving the registered mobile device identifier, the backend server pushes such to the set-back box associated with (e.g., resides in) the checked-in structure. The set-back box is enabled (e.g., BLE enabled) to actively scan addresses of nearby mobile devices. When the registered mobile device identifier is detected within a predetermined signal strength range (e.g., by using received signal strength indicator (RSSI) levels), the set-back box transmits a command to a smart lock (e.g., via BLE or Wifi or other radio) or to a lock controlling backend processor, to open the lock.