When GPS is denied or spoofed, the pendant switches to an on-device vector-map that fuses accelerometer, gyro, and barometer data to calculate dead-reckoned waypoints. A Kalman filter continuously refines position error, allowing hikers, first-responders, or disaster teams to navigate canyon, forest, or urban canyon environments for up to 72 h without satellite lock. If a mesh neighbour has a valid fix, the filter ingests that telemetry (encrypted, zero-knowledge) to reset drift—no central server required.