A continuous glucose monitor (CGM) is a wearable device that automatically tracks blood glucose levels at all times, day and night.
It uses a small sensor placed under the skin, often on the arm or stomach. This sensor measures the interstitial glucose level, or the amount of glucose in the fluid between cells. The continuous glucose monitor tests glucose levels every few minutes, and its data is then transmitted wirelessly to a monitor.
Sometimes, a continuous glucose monitor is combined with an insulin pump, which injects insulin based on the recorded glucose levels.
Some continuous glucose monitors require calibration twice a day. For this, the user tests a drop of their blood on a standard glucose meter and compares it to the continuous glucose monitor to ensure they are close.