A blowout preventer for sealing a tubular of a wellbore is provided. The blowout preventer has a housing having a bore therethrough for receiving the tubular, at least one ram slidably positionable in the housing (each of the rams having a ram block for sealing engagement about the tubular), an actuator for selectively driving the ram block (the actuator comprising a piston slidably positionable in a cylinder), and a monitor for detecting the piston therein. The monitor has a visual indicator on an exterior of the cylinder. The visual indicator is operatively coupled to the piston for displaying a position of the piston as the piston travels within the cylinder whereby a position of the ram may be determined.