1. A monitoring system, comprising: one or more cameras to determine a three dimensional (3D) body model of a person; a processor coupled to the one or more cameras to process the 3D body model to detect a dangerous condition based on the 3D model with computer readable code to detect the person's fall including: computer readable code to detect a falling speed of the person's center-of-mass (threshold 1); computer readable code to detect when a body part touches a floor; and computer readable code to detect a time span without center-of-mass motion after fall (threshold 2); and a device to generate a warning when the dangerous condition is detected.