Abstract: A system for decoding locks having a sequence of spring-urged sliding members such as tumbler pins or wafers includes a probe device having the general contour of a key having a head portion and a straight shank fabricated of electrically insulative material and terminating in a tip portion having an oblique ramp surface. A series of spaced apart electrical conductors embedded within the shank in parallel relationship extend from the head portion to the ramp surface where they emerge as electrical contacts. An electrical circuit which includes an electronic monitoring and display apparatus detects when a given sliding member touches a most distant electrical contact, thereby representing a travel distance. The travel distance is correlated with a particular pin or wafer to produce the key code for the lock.