Methods, systems, computer-readable media, and apparatuses for obtaining blood pressure measurements are presented. The blood pressure measurements may be obtained by determining a pulse-transit time (PTT) as a function of a photoplethysmography (PPG) measurement and electrocardiogram (ECG) measurement. A mobile device includes outer body sized to be portable for a user of the mobile device. The mobile device also includes a plurality of light emitting components distributed along at least one portion of the mobile device and a plurality of light collecting components configured to measure reflected light from the plurality of light emitting components reflected off of blood vessels within the user. The light emitting and light collecting components are distributed along the at least one portion of the mobile device. The mobile device may also include a light guide configured to direct light emitted by the at least one light emitting component toward blood vessels with the user.