Abstract: A lock mechanism having a casing through which a spring-biased bolt is slidably movable, the bolt having an end which can be normally extended for a relatively short distance beyond the casing to assume a so-called "latching" position. A slidable sensing bar is arranged alongside of the bolt and in sliding contact therewith and the sensing bar is spring-biased so that it normally projects out of the casing for a distance co-extensive with the bolt while the bolt is either retracted or is in its latching position. A roller carried by the bolt is interposed between the bolt and the sensing bar and is confined in the casing in such a manner that while it rests upon a cam portion of the sensing bar, its bodily movement in the casing will be limited by a stop located therein and the bolt and the sensing bar will be maintained together in either the fully retracted position of the bolt or in its latching position.