B. Set up of Single Mobile Phone for Blood Pressure Estimation In this setup,we record heart sounds with a customized external microphone and finger pulse at 24 fps via a video and audio recording application. An LED flash lights up when the application starts and then the start-time of video and audio recording are saved in the phone’s SD card. The design of the external microphone consists of an acoustic stethoscope diaphragm, hollow tube, 3.5 mm mini-plug condenser microphone with frequency response 50–18,000 Hz and a 3.5-mm microphone adapter for mobile phones. We fix the diaphragm to one end of hollow tube and microphone to other end of the hollow tube. Fig. 3 shows the customization of external microphone. This customized microphone replaces the need for the second mobile which is used to measure heart sounds in Fig. 1.