A. Setup of Two Mobiles for Blood Pressure Estimation Inthe firsttechnique, thesetup startswithsynchronization of time between two mobile phones using Bluetooth. After syn- chronization, the camera on one mobile records the pulse in the finger at 24 frames/s (fps) via a video recording applica- tion. An LED flash lights up when the application starts and then the start-time of video recording is saved in the phone’s SD card. Similarly, the second mobile starts recording the heart sounds via the audio recording application with the phone’s microphone held close to the chest. Care has to be taken that the microphone’s opening is held tightly to the skin over the chest to avoid recording external noise. Fig. 1 shows the overall procedure of the differential estimation technique.