In any critical infrastructure, the question is not if a disruption will occur, but when.
The average cost of just one hour of downtime, as reported by over 90% of enterprises, is over $300,000 (source). For a security system, the cost extends beyond the financial, impacting both physical safety and asset integrity.
This article addresses the engineering required for resilience. The reliability of a modern access system is defined by its performance under adverse conditions and rests on three pillars of engineering: graceful software degradation, multi-layered backup power, and non-negotiable emergency overrides.
Graceful Degradation: Maintaining Core Functionality Offline
When a UWB lock loses network connectivity, its architecture must immediately shift from centralized intelligence to autonomous operation. The primary security function—validating an authorized user—must remain intact.
From Centralized to Edge Autonomy
The system must be designed for an instantaneous transition. During regular operation, a central server manages access decisions and live audit logging. In an offline state, this entire logic is handled by the lock’s onboard microcontroller.
This is a pre-programmed, fully autonomous state of operation that maintains the core security promise without requiring any user intervention or awareness of the backend failure.
Secure Credential Caching and Local Authentication
This autonomy is enabled by secure credential caching. The lock’s internal secure element (SE) or a trusted execution environment (TEE) stores an encrypted, rotating list of authorized credentials.
When a user presents a UWB device, the lock performs the complete Time-of-Flight (ToF) distance measurement and cryptographic challenge-response sequence locally. It validates the credential against its secure cache, making an authoritative access decision in milliseconds without a network query.
State Synchronization Post-Disruption
Once connectivity is restored, the lock must intelligently re-synchronize its state with the central server.
- Buffered Event Logs: All access events (grants and denials) that occurred during the outage are timestamped and buffered in local memory. Upon reconnection, this queue is uploaded to maintain a complete audit trail.
- Conflict Resolution: The system must resolve potential conflicts, primarily concerning credential revocation. The protocol must prioritize pulling the latest access control list (ACL) from the server, ensuring a credential revoked during the outage is immediately invalidated on the lock, even before the full event log is uploaded.
Designing a Multi-Layered Backup Power Strategy
Relying on a single internal battery for a UWB access point is an insufficient and high-risk strategy. A reliable design implements a tiered approach to power redundancy.
Tiered Power Redundancy
A multi-layered strategy ensures operation across different failure scenarios, from a tripped breaker to a grid-level outage. Each subsequent tier provides a higher level of availability for the lock’s core function.
Tiered Power Redundancy Strategy for UWB Systems:
Low-Power Firmware and Battery Chemistry
Hardware and firmware must be engineered for extreme power efficiency. In a power-fail state, the lock must enter an ultra-low-power mode, consuming microamperes. The high-draw UWB radio should only be activated for the brief sub-second interval required for ranging and authentication. The choice of battery chemistry is key:
- Lithium Thionyl Chloride (Li-SOCl₂) offers a very high energy density and an extremely long shelf life (over 10 years), making it ideal for “fit-and-forget” deployments where the battery is primarily for emergency use.
- Lithium-ion Polymer (Li-Po): A rechargeable option suitable for locks where frequent, short power interruptions are expected and mains power can be used to recharge the cell.
Predictive Power Management
A truly smart system manages its backup power proactively.
The lock’s firmware should continuously monitor and report its battery voltage and health to the central server. This data enables predictive maintenance, generating an automated service ticket to replace a battery before it fails, transforming maintenance from a reactive emergency to a scheduled, low-cost task.
The Non-Negotiable Need for Emergency Override Procedures
In a scenario of catastrophic electronic failure, a clear, reliable override procedure is the final layer of security and operational continuity.
High-Security Mechanical Override
For any critical door, the ultimate failsafe is a physical key. Integrating a high-security mechanical lock cylinder (e.g., an ANSI/BHMA A613 Grade 1 certified cylinder) is a non-negotiable requirement.
This provides a guaranteed method of access that is completely decoupled from the electronic systems, ensuring access for emergency responders or technicians.
Secondary Digital Access via NFC
A secondary digital path provides resilience against the failure of a primary technology.
Incorporating an NFC reader offers a key advantage: parasitic power. A user can hold an NFC-enabled phone or card to the reader, and the lock can harvest enough power from the phone’s NFC field to energize its microcontroller, validate the credential, and actuate the lock—even if the lock’s internal battery is completely dead.
Auditable Administrative Credentials
Break-glass scenarios require special administrative credentials (e.g., a master UWB fob) that can override standard access rules.
The use of such a credential must be a high-priority, immutable event in the system’s audit log. The management of these physical master keys, including their storage and authorized users, is a vital component of the overall security policy that must be defined during system deployment.
Conclusion: Engineering Trust as the Core Feature
The true resilience of a UWB access system is defined by its predictable, reliable behavior during failure. A system that gracefully degrades to an autonomous state, is supported by a multi-layered power strategy, and provides clear override procedures, is a cohesive failsafe architecture.
These three pillars—software autonomy, hardware endurance, and procedural integrity—must be engineered in concert to eliminate single points of failure.
Ultimately, the adoption of advanced technology for critical infrastructure, like access control, depends entirely on trust. This trust is earned when the system is tested by disruption.
By designing for failure, we build systems that protect assets, ensure human safety, and guarantee operational continuity without compromise. When evaluating any access control solution, one of the most important questions is whether it has engineered foresight for the inevitable. That resilience is the true measure of a secure investment.
