News, reviews & insights into your choice of continuous glucose monitors.
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What is a CGM?
5 August 2025
Date Published:
Often abbreviated to CGM, Continuous Glucose Monitors are now a tool for wellness as well as diabetes management. Coming at this from a non-medical view of the system, we provide experience-based insights that equally apply when referring to a 'sensor', 'biosensor' and 'wearable' for measuring glucose levels.
Let’s start with the basics as we’re often being dazzled with scientific terms or over-complicated explanations.
CGM stands for continuous glucose monitoring. It is basically a sensor that sticks to your arm to measure glucose levels and these are shown on an app. Using a CGM enables users to monitor their glucose levels continuously 24/7.
A sensor, for example Freestyle Libre, is intended to last 15 days and you keep this attached to your skin – usually visible on the upper arm – for the whole time. If dislodged, knocked off or taken off it stops working and can’t be restarted.
Before you ask…there is a needle, but this is only used to insert a small filament into the skin that takes measurements from the fluid around the cells just under the skin. The needle is only used as part of the application process and it retracts back into the applicator once the filament has been inserted.
Additionally, the measurements recorded by the sensor are sent by Bluetooth to an app and an algorithm converts the data into glucose levels that the wearer can see on a graph (or static reading). Glucose levels are usually updated continually in real-time.
Some of the CGM options available (in the UK) are FreeStyle Libre, Dexcom and GlucoRx.
Note, some persons with diabetes use a CGM reader instead of smartphone.
