CGM Sensors Compared

Shopping for a continuous glucose monitor can feel confusing, because sensors differ along several dimensions at once — how they calibrate, how they deliver data, and how they are worn. This guide compares the main categories at a neutral, general level and names the major makers, without quoting current specs or prices, since those change often. It is a map of the landscape, not a ranking. For the foundation, see the CGM guide.

Factory-calibrated vs calibration-required

One useful way to divide CGMs is by calibration — how the system is kept aligned to a reference glucose value.

• Factory-calibrated sensors arrive pre-calibrated from the manufacturer and generally do not require the user to enter finger-stick values. This reduces day-to-day effort, though a finger-stick may still be advised to confirm readings in certain situations.
• Calibration-required sensors ask the user to periodically enter a finger-stick blood-glucose value so the system can adjust itself. This adds a small routine but is how some devices maintain alignment.

Neither approach is universally "better" — they represent different design trade-offs. Why calibration exists at all connects to how sensing works, which we cover in how a CGM works, and it also relates to the broader accuracy discussion in how accurate is a CGM.

Real-time vs intermittently scanned

A second way to categorize CGMs is by how you get the data.

• Real-time CGM (rtCGM) streams readings automatically to a phone or receiver and can push alerts, for example when glucose is heading high or low, without any action from the user.
• Intermittently scanned CGM (isCGM), sometimes called flash monitoring, stores readings continuously but displays them when the user scans the sensor with a phone or reader. Some products in this category have added optional automatic alerting, so the line between the two has blurred over time.

The practical difference is whether readings and alarms come to you automatically or when you check. That distinction can matter for anyone relying on alerts, and it feeds into choosing a CGM.

Skin-worn vs implantable

Most CGMs use a small filament inserted just under the skin and worn for a set number of days before replacement. A different category is the implantable sensor, in which a longer-lasting sensor is placed under the skin by a clinician in a brief procedure and paired with an external transmitter worn on top. Implantable options are designed for extended wear measured in months rather than days, at the cost of an in-office insertion and removal.

Both approaches produce the same fundamental output — a continuous glucose trace — and the choice comes down to preferences around wear length, convenience, and clinical fit rather than one being inherently superior.

The major names

A handful of manufacturers account for most CGMs in use today. Named here for orientation only, with no endorsement and no current specifications:

• Dexcom — known for real-time, factory-calibrated systems.
• Abbott FreeStyle Libre — a widely used line that began as scanned monitoring and has expanded its feature set.
• Medtronic — offers CGM often paired with its insulin-pump ecosystem.
• Senseonics Eversense — known for an implantable, longer-wear sensor.

Each company offers multiple products, and their designs, features, wear times, availability, and prices change frequently and vary by region. For anything specific — current models, compatibility, accuracy claims, or cost — check the manufacturer's own site and confirm with your clinician and insurer. Whatever sensor produces the data, clinical software such as Endobits is designed to help a clinician interpret glucose patterns as decision support under professional oversight, not to diagnose or treat on its own.

How to weigh the options

Because the categories overlap, the useful questions are practical: Do you want automatic alerts, or is scanning fine? How long would you like a sensor to last? Do you mind occasional calibration? Which app and devices does it work with, and what does your coverage support? Working through these — ideally with a clinician — matters more than any single spec. Choosing a CGM and the glossary can help you frame the conversation.

Sources

U.S. Food and Drug Administration, Glucose Testing Devices. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Continuous Glucose Monitoring. American Diabetes Association, Devices & Technology.

Related: The CGM guide · Choosing a CGM · How a CGM works