Continuous glucose monitor
A continuous glucose monitoring (CGM) system is a medical or wellness device used to continuously track interstitial glucose levels in real time, replacing the need for periodic finger-stick blood draws. Tracking interstitial glucose is a valid way to monitor blood glucose due to their high correlation, despite a lag time in glucose levels between the interstitial space and the bloodstream.
Source: Wikipedia — Continuous glucose monitor (CC BY-SA 4.0)