1. A method for determining pulse transit time (PTT) non-invasively, the method comprising: generating an electrocardiogram (EKG) for a user of a handheld device, wherein the EKG is generated from two conductive contact points on the handheld device in contact with two portions of the user's body; de-noising the EKG to identify a start time of the PTT, the start time of the PTT being a time when a blood pulse leaves a heart of the user; receiving a plurality of video images of the user; finding the user's face in the plurality of images; cropping the plurality of images to generate cropped images that include the user's face; de-noising the cropped images to identify a pressure wave indicating an arterial site and an end time of the PTT, the end time of the PTT being a time when the pressure wave appears; determining the PTT by computing a difference between the start time of the PTT and the end time of the PTT; and determining a blood pressure measurement for the user based on the PTT.