Abstract: A pet door system for allowing pets to enter and exit a building is provided. The pet door system comprises a pet door having a top edge, a pair of side edges, and a bottom edge with the pet door pivotally mounted within the opening. An aperture is formed in the top edge only of the pet door. A groove extends from along each side of the aperture. A plunger is moveable into and out of the aperture with the plunger riding in the groove. A solenoid moves the plunger into and out of the aperture with an activation mechanism activating the solenoid. Upon the activation mechanism being positioned within a predetermined distance from the pet door, the solenoid causes the plunger to automatically unlock the pet door. Upon the activation means being positioned outside the predetermined distance from the pet door, the solenoid causing the plunger to automatically lock the pet door.