Electronic locks was not a thing in 1900. Old cars with manual locks did indeed have the cases where the driver reaches over and locks the passenger door, when

Electronic locks was not a thing in 1900. Old cars with manual locks did indeed have the cases where the driver reaches over and locks the passenger door, when the passenger forgets to lock it themselves. And users of old cars will remember the "open front door, reach inside and unlock back door" maneuver.