Lockbox Hail-Triggered Transponder Authentication
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Solution Overview
Problem
Previous electronic lockbox systems face battery drain issues due to constant listening for radio or light beam messages, leading to limited battery lifetime and inconvenience, especially when cellular communication links are used, resulting in potential lockbox inoperability during property showings without a spare battery.
Innovation Solution
An electronic lockbox system that includes a wireless portable transponder, where the lockbox sends a hail message via low power radio, and the transponder responds with an encrypted message, with the lockbox authenticating using its own encryption key, and the transponder stores access event records, which are then sent to a central clearinghouse computer when a wide area network is available, and the system temporarily disables the electronic key if the dwelling key is not returned to its original lockbox.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the lockbox constantly listens for radio or light beam messages, then access responsiveness is improved, but battery lifetime deteriorates
Solution Approach 1:
The lockbox transitions from continuous listening to periodic communication initiated by hail messages. The system remains in a low-power state until triggered by an external hail message, then activates for the authentication sequence and returns to sleep mode, creating periodic rather than continuous operation cycles
Solution Approach 2:
The portable transponder actively initiates communication by sending hail messages to the lockbox, rather than the lockbox continuously waiting for messages. This reverses the communication initiation role, allowing the lockbox to remain powered down until needed
2Reliability
If cellular communication links are used for real-time data transmission, then security monitoring is improved, but energy consumption increases
Solution Approach 1:
Access event records are transmitted periodically when the portable transponder next communicates with the system, rather than transmitting continuously or in real-time. This reduces the frequency of high-energy cellular communications while maintaining security monitoring capability
Solution Approach 2:
The system accepts delayed transmission of access event records rather than requiring immediate real-time transmission. Records are queued and transmitted when communication opportunities arise, accepting temporary local storage rather than continuous connectivity
3Reliability
If the electronic key is disabled after dwelling key removal, then security against unauthorized use is improved, but operational flexibility deteriorates
Solution Approach 1:
The system monitors the location of the dwelling key through sensor feedback. When the dwelling key is detected in a different lockbox than the one it was originally paired with, the system automatically disables the electronic key, creating a feedback-based security mechanism that adapts to the physical state of the system
Solution Approach 2:
The system performs preliminary verification of dwelling key location before allowing electronic key operation. By checking whether the dwelling key is in its expected lockbox before enabling access, the system prevents unauthorized use while maintaining flexibility for legitimate multi-lockbox scenarios
Data Source
AI summary
An electronic lockbox system includes a wireless portable transponder that communicates with an electronic lockbox using a low power radio link. The portable transponder includes: a wide area network radio to communicate to a central clearinghouse computer, a motion sensor to activate its wide area network radio, and a connector to communicate with a secure memory device. The electronic lockbox sends a hail message that is intercepted by the portable transponder; the hail message includes identification information. The portable transponder responds with a message that includes a time sensitive encryption key; the lockbox authenticates this response message using its own time sensitive encryption key. If an electronic key is used to access the lockbox, the improved system effectively disables the electronic key during a showing, so that the electronic key cannot be used to access another lockbox until the correct dwelling key has been placed back into the lockbox.