US Patent 10001808 Mobile device accessory equipped to communicate with mobile device

A smartphone case can include one or more piezotransductive materials (e.g., piezoelectric, piezomagnetic, piezoluminescent, etc.) positioned at one or more contact locations of the smartphone case. For example, a piezoelectric material can be positioned at multiple different locations of the smartphone case at which users may physically contact the smartphone case when holding the case. The piezoelectric material can generate an electric charge when pressure is applied to the material, and the generated electric charge can pass through an electromagnetic coil as an electric current to produce a magnetic field which one or more sensors (e.g., one or more magnetometers) of a smartphone that is housed within the smartphone case may be able to detect.