A lock (1) comprises at least a bolt (7) actuated by means of a flexible shape memory element (14), which can take an extended and a shortened configuration as a result of heating. Constraint means (P, 10, 17) cause the arrangement of at least an intermediate portion of the shape memory element (13), within which portion said element is associated to the bolt (7); the constraint means (P, 10, 17) are in such relative positions that said intermediate portion of the shape memory element (14) takes a substantially V-shaped arrangement at least when the first controlled element (7) is in its operating position.