Usually measured through obtrusive contact-based methods, heart rate (HR) and peripheral oxygen saturation (SpO 2 ) are critical physiological signs used by clinicians during emergency interventions. Remote Photoplethysmography (rPPG) allows for unobtrusive sensing of these vital signs for health monitoring in various settings. We present a review of rPPG-related research conducted including related processes and techniques, such as regions of interest (ROI) selection, extracting the raw signal, pre-processing data, applying noise reduction algorithms, Fast Fourier transforms (FFT), filtering and extracting these vital signs. Further, we present a detailed, critical evaluation of available rPPG systems. Limitations and future directions have also been identified to further advance this field.