A portable electronic device may include a housing member defining a side surface of the portable electronic device, a portion of the housing member defining a side wall of a hole extending through the housing member, a button member positioned along the side surface and defining a chassis portion and a hollow post extending into the hole defined through the housing member, and a first waterproof seal defined between the hollow post and the side wall of the hole. The portable electronic device may also include a biometric sensing component coupled to the chassis portion, a flexible circuit element extending through the hollow post and conductively coupling the biometric sensing component to a component within the housing, and a second waterproof seal defined within the hollow post.