An elevator car door safety device that uses flags along a hoistway is disclosed. The elevator car door safety device is mounted to the outside of an elevator car door using a mounting plate and includes a locking assembly mounted to the sill of the elevator car door. The car door safety device includes a lever with a hook at its distal end. The safety device also includes a flag engagement arm perpendicularly mounted to the lever. If the flag engagement arm engages a flag on the hoistway then the hook is prevented from being lodged into the locking assembly and the car door is permitted to open. Inversely, if no flag is engaged, the lever will continue to rotate urging the hook to be lodged within the locking assembly, thereby preventing the door from opening. An electric switch assembly can be used to stop the motion of the elevator.