Systems and methods for switching to a back-up power supply are provided. The upper resilient member and lower resilient member may be attached to one another by a flexible substrate having a middle portion that is narrower in length than the upper or lower resilient members. A ramped bias field enables the position of the sensitive region of the sensor to be controlled, for measuring local stress, or for mapping an external magnetic field. A communication unit 22 communicates with the electronic device over a network based on the identification information.