Abstract: A monitoring apparatus for pressure sensitive devices is provided which detects the operating state of the monitored device, and which is designed to provide a reliable output even when operated in hostile, corrosive environments. The monitoring apparatus preferably includes a light source for transmitting a beam of light along a path of travel proximal to the monitored device, a light detector for detecting the light beam, and a member for adjusting the path of travel of the light beam in response to the actuation of the pressure sensitive device. Several alternative embodiments are disclosed.