If your car doors lock automatically when you drive, it means that your vehicle has a feature called auto-lock. This feature is a safety measure taken by automobile companies. This feature locks all the doors of the car, as soon as the first gear is engaged, so that young children don’t accidentally open the door while the car is not stationery. However, not all cars have this feature. Some cars have speed sensing door locks, which is essentially the same thing, but the doors are locked when the car breaches a defined speed. Generally, the defined speed is 10 km/h, or around 6 m/h.