A continuous glucose monitor (CGM) is a tiny wearable device that reads your glucose levels. It is attached to your body (usually worn on the upper arm or on the stomach) and continually monitors how much glucose you have circulating in your body at any time. A CGM has two parts - a sensor and a transmitter. The sensor is worn just under your skin and the transmitter sends results to a wearable device or to your cell phone. You keep the continuous glucose monitor on at all times, including in the shower, when getting your sweat on, and when you sleep.
For more information on CGMs and how they work, see How Does a Continuous Glucose Monitor Work?