The present invention relates to a hold-open apparatus for controlling the position of a door, preferably a screen door or storm door. The apparatus is used in conjunction with a piston assembly and can maintain a door in a predetermined open position, such as about 45 to about 100 in relation to a closed position. In a preferred embodiment, the apparatus can automatically lock and/or unlock when the door reaches predetermined positions. The apparatus advantageously can be retrofitted to existing door assemblies.