Abstract: Methods and apparatus for decoding twisting tumbler locks and improvements in such locks to resist such methods and apparatus. To determine depth of cut of bit for a given tumbler, a blade is inserted into key way to position a wirelike probe at tumbler to be decoded. Wirelike probe is advanced upwardly until it engages tit at top of tumbler. Depth of cut of key bit is function of length of tumbler and device can be calibrated to give direct readout of depth of bit cut. Angle of key bit can be measured by hooking a wirelike probe in side gate groove in tumbler and then twisting tumbler until tit engages key plug or shell. Amount of twist permitted is function of angular position required to register tumbler groove with side gate and device can be calibrated to give direct reading of such angle. To defeat depth of cut decoder, twisting tumbler lock wherein tits on tumblers are located at different distances from tops of tumblers is disclosed.

Abstract: Method and apparatus for decoding twisting tumbler lock of the type wherein side bar is sole locking element and normally bridges shear plane unless radial apertures in twisting tumblers are all in vertical and horizontal register with complementary side bar protrusions. Decoding apparatus comprises three devices each with a blade insertable in keyway and having upwardly and rearwardly sloping front surface angulated at one of three angles to which tumblers must be twisted for horizontal registration of apertures. Each blade has indicia for indicating that front surface is at particular tumbler and further has indicia for determining amount of elevation of tumbler resulting from camming action between chisel shaped tumbler bottom and blade front surface when blade is advanced from initial engagement with tumbler to elevate tumbler.