Methods, systems, computer-readable media, and apparatuses for obtaining vital measurements are presented. The vital measurements may include a blood pressure value that can 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 an outer body sized to be portable for a user, a processor contained within the outer body, a display coupled to a light guide, and at least one first sensor coupled to the light guide. The display is configured to display an illumination pattern directing light toward blood vessels within the user. The at least one first sensor is configured to measure reflected light from the illumination pattern reflected off of the blood vessels within the user, wherein the processor is configured to obtain a first measurement indicative of changes in blood volume based at least in part on the measured reflected light.