Abstract: A pin and tumbler type lock in which a slide element is disposed at that end of the cylinder opposite the end from which the key is inserted, the slide element cooperating with a pin in the barrel and having a projecting portion diametrically opposite to the pin with which it cooperates which, in the locked condition, engages in an opening of the barrel. The slide element has a configuration for cooperation with the leading end of a key so that insertion of the correct key causes disengagement of that portion of the slide extending into the opening in the barrel and additionally brings abutting portions of the slide element and the cooperating pin to a shear line between the cylinder and the barrel to free the lock. Additionally, at least one pin in the lock has an electrically conductive extension adapted, when the pin with which it is associated is raised beyond the shear line to complete a circuit to an alarm device.