The CGM sensor is typically inserted into the subcutaneous tissue, usually on the abdomen or the back of the upper arm. It's a minimally invasive procedure similar to inserting an insulin pump infusion set or a small needle. Some CGM systems have a disposable sensor that needs to be replaced every few days, while others have a longer lifespan.

Once inserted, the sensor continuously measures the glucose levels in the interstitial fluid. This measurement happens at regular intervals, usually every few minutes. The sensor uses a process called enzymatic reaction to detect glucose levels. An enzyme reacts with glucose in the interstitial fluid, producing a signal that is then measured by the sensor.

The sensor is connected to a transmitter, which wirelessly sends the glucose data to a receiver or a smartphone app. The transmission range varies depending on the CGM system but is typically within a few meters.

The receiver or smartphone app displays the glucose data in real-time. Users can see their current glucose level, trends over time, and alerts for high or low glucose levels. Some CGM systems also provide predictive alerts, warning the user if their glucose is likely to go out of range in the near future.

CGM systems can be customized to provide alerts and alarms for various glucose levels. For example, users can set thresholds for high and low glucose levels, and the system will alert them if their glucose goes above or below these thresholds. This feature is particularly helpful for managing hypoglycemia (low blood sugar) and hyperglycemia (high blood sugar) and reducing the risk of diabetes-related complications.

CGM systems store glucose data over time, allowing users and healthcare providers to review trends and patterns in glucose levels. This data can be used to adjust insulin dosages, diet, and lifestyle factors to better manage diabetes.