An electronic device can include a housing, a back cover, a structural member, and a sensing circuit. The housing can at least partially define an internal volume of the electronic device and the back cover can define at least a portion of the internal volume and be connected to the housing. The structural member can be disposed against the back cover and at least partially within the internal volume, the structural member including an electronic component. The sensing circuit can be disposed in the internal volume and electrically coupled to the electronic component. The sensing circuit can detect an amount of charge of the electronic component as part of a user proximity sensor of the electronic device.