Shared micromobility, particularly rental e-scooters, has rapidly transformed urban transportation. Voi Technology has been at the forefront of this shift, powering over 300M rides across Europe. While most customers use the service responsibly, mitigating reckless riding emerges as a significant challenge given the high ridership. Previous research shows that riders taking indirect routes are more likely to be involved in safety-critical events, suggesting potentially irresponsible riding behavior. However, directness alone can overlook important intra-trip patterns. Therefore, in this study, we use GNSS positioning as a proxy for intra-trip riding behavior. We model a typical ride as a sequence of turning angles derived from GNSS coordinates and detect anomalies leveraging the testing-by-betting framework, which provides formal guarantees on false positive rates while achieving a favorable trade-off with false negatives. The presented method is designed to operate under limited onboard compute, with minimal complexity for deployment across large vehicle fleets, without requiring the GNSS trace to be stored—a key privacy advantage. In a real-world evaluation, the method detects approximately 60% of reckless rides while maintaining operationally acceptable false positive rates.