A package comprises a body having a mounting surface so as to be mounted to an external surface, and a coil having at least 100 turns around a coil axis. A first end of the coil is oriented in a first direction substantially parallel to the mounting surface such that the first end is attachable to the external surface. The package includes a ferromagnetic element that extends along the coil axis such that the ferromagnetic element is magnetically coupled to the coil. The body is configured to house the coil and the ferromagnetic element.