all of the circuitry can be encapsulated in a protective material in one embodiment a flexible circuit board provides connections to all the switches to the leds to the logic circuit and to the battery fig9 shows schematically another embodiment of a ring 902 that is similar to that of fig7 but the embodiment of fig9 uses mercury switches 904 as a nozzle not shown is inserted element 906 is displaced changing the angle of the floor of switch 904 and causing the mercury 908 to flow and electrically connect first contact 910 and second contact 912 fig1 shows another embodiment of the invention in which a displaceable mechanical elements 1002 provides the electrical contact a nozzle in a gasoline pump is grounded when the nozzle is inserted it electrically grounds the element 1002 completing the circuit in any of the embodiments sparks can be reduced or eliminated by the use of low voltage dc contacts and the use of an appropriate u201c spark quencher u201d circuit having appropriate inductance and capacitance to dissipate any energy slowly to avoid a spark fig1 shows a nozzle 1102 of the correct size being inserted into the filler neck 1104 to which a sensor ring 1106 with displaceable mechanical elements 1107 is attached because the nozzle 1102 displaces all of the displaceable mechanical elements 1107 of the sensor ring 1106 indicators 1108 are not lit up fig1 shows a nozzle 1202 having a diameter smaller than the proper diameter for the type of fuel required fig1 shows that the nozzle 1202.