A continuous glucose monitor (CGM) has two parts. You wear one part—the sensor—against your skin. It has a tiny needle that stays under your skin and constantly reads your blood sugar level. It sends this information to a wireless receiver. The receiver can tell you if your blood sugar is going up or down—and how fast. And you can view the stored data on a computer to help you identify trends in your blood sugar level.

CGMs communicate with some blood glucose meters and even insulin pump systems. All CGMs need to be calibrated regularly with a blood glucose meter to be sure the readings are accurate.