A lock mechanism having a cylinder normally held against rotation to an unlocking position by two sets of pin tumblers disposed at opposite sides of the cylinder axis. One set is of the conventional type comprising a number of pin tumblers and drivers therefor actuatable to cylinder releasing positions by the bitting on one edge of a key inserted into a keyway in the cylinder. The other set of tumblers is comprised of a number of magnets arranged in a row lengthwise along the other edge of a key in the keyway, and repelled to cylinder releasing positions by magnet members on the key.