The invention represents the disclosure of a novel automatically activated device that locks the wheels of a wheelchair, to prevent backward motion of the chair when the occupant arises, reducing the risk that the chair's occupant may fall due to the backward motion of the chair. The device is activated when the occupant leaves the seated position And the device is inactivated when the occupant resumes the seated position in the chair, allowing the wheels again to move freely. The device, which is designed to be installed upon existing wheelchairs, and newly manufactured wheelchairs, includes a disabling device, enabling free movement of the wheelchair when unoccupied.