A device having a base element affixed to or for affixing to a frame of a bicycle, a helmet-engaging element for passing through an aperture in the helmet in order to secure it, which is attached to or mounted on the base element and moveable between stowed and operational configurations and a locking element for locking to at least a part of the engaging element provides a helmet locking system which may fit or adapt to any bicycle and enables any cycle helmet having ventilation holes to be locked to the bicycle when not in use, without the need to carry additional equipment and regardless of who is riding the bicycle or which helmet they are using.