Your MDC10W is equipped with a G-sensor that detects shocks. Each time an impact is detected, it will lock the recording during which the event occurred and prevent the loop recording from being overwritten. The sensitivity is set to Low by default, but can be set to Off/High/Medium/Low. A Low setting means it requires the most impact to trigger the 'locking' of recordings, while a High setting requires the least impact to trigger the 'locking' of recordings.