Piston actuators and methods of its operation are described. The piston actuators include a housing defining a chamber having a piston therein and a spring seated against the piston to bias it into a starting position. The piston includes a ferromagnetic material, a magnet or both and a secondary magnet or ferromagnetic material, forming a first magnetic/ferromagnetic pair with the piston, is positioned to maintain the piston in a secondary position. A tertiary magnet or ferromagnetic material, forming a second magnetic/ferromagnetic pair with the piston, may assist the spring in maintaining the piston in the starting position. During operation, introduction into or removal from the chamber of an amount of fluid sufficient to overcome the force of the spring (and the tertiary magnet or ferromagnetic material) enables the attraction between the members of the first magnetic/ferromagnetic pair to move the piston to the secondary position as a snap movement.