the two surfaces 130 and 132 and the surfaces 130 and 132 are generally disposed at 45 degrees from the optical fiber ends 124 and 126 respectively it is therefore to be understood that light emitted by the leak detector emitter optical fiber tip 125 will reflect downwardly from the first surface 130 towards the second surface 132 and then rearwardly from the surface 132 to the tip 127 of the leak detector receiver optical fiber 26 however should a fluid come in contact with the window 90 it will cause a change in the optical path of the reflecting beam due to the different index of refraction of the fluid from air at the exterior surface of window 90 whereby the light beam from the emitter tip 125 will no longer be received at the receiver tip 127 when this condition occurs the electro optical transceiver 28 ceases sending electrical signals to the controller 22 and an alarm is sounded which indicates that fluid has contacted the window 90 as an indication of a leak in the fluid handling device into which the detector plug 12 is inserted the thickness of window 90 and particularly the window section 132 must be such that the window can withstand the relatively high pressure that is sometimes generated within a fluid handling device yet thin enough to provide good optical refraction characteristics when a leaking fluid contacts the exterior surface of the window in the preferred.