A Continuous Glucose Monitoring (CGM) system is a device used to measure glucose levels in real time, continuously. Continuous glucose monitoring (CGM) shows the glucose value in a completely different way than an ordinary blood glucose meter - which provides only a single value for a single time - by finger-prick test. Plus the trend and the speed at which the glucose levels are going up or down. It also has a range of alerts and alarms and other features that allow better control of diabetes with less risk.