For millions of people managing diabetes, the decision to use a Continuous Glucose Monitor (CGM) is a major step toward better health and greater freedom. These devices provide dynamic, real-time insights into glucose levels, replacing the guesswork of finger-prick checks with data that reveals trends, patterns, and alerts you to highs and lows before they become problems. But not all CGMs are created equal. Choosing the right one depends on your lifestyle, budget, comfort with technology, and how you interact with your diabetes every day. This guide breaks down the different types of CGMs on the market, explains how they work, and walks you through the key factors that will help you select the best device for your needs.

What is a Continuous Glucose Monitor (CGM)?

A Continuous Glucose Monitor is a wearable device that measures glucose levels in the interstitial fluid—the fluid just beneath the skin—every few minutes, day and night. The system consists of three main components: a tiny sensor inserted under the skin (usually on the abdomen or arm), a transmitter that sends data wirelessly, and a receiver or smartphone app that displays the readings. Unlike a traditional blood glucose meter, which gives only a single point-in-time measurement, a CGM shows your glucose direction and speed of change, helping you anticipate what’s coming next.

Most modern CGMs are approved for making treatment decisions—meaning you can dose insulin or treat hypoglycemia based on the CGM reading without a confirmatory finger stick. This has transformed diabetes management for both type 1 and type 2 diabetes. According to the American Diabetes Association, using a CGM can lower A1C levels and reduce hypoglycemic events, especially in people who take insulin. The technology continues to evolve, with newer models offering greater accuracy, longer wear times, and seamless integration with insulin pumps and smart devices.

Types of Continuous Glucose Monitors

The CGM landscape can be divided into three primary categories: real-time CGMs, flash glucose monitoring systems, and professional (blinded) CGMs. Some newer implantable devices also blur the lines between categories. Understanding the differences will help you match a device to your daily routine.

Real-Time CGMs

Real-time CGMs (rtCGMs) automatically send glucose data to a display device—typically a smartphone or a dedicated receiver—without any action required from the user. The display updates every one to five minutes, showing the current glucose number, a trend arrow indicating direction of change, and a graph of recent readings. These systems provide customizable alarms for high and low glucose thresholds, as well as alerts for rapid changes in glucose levels. Leading examples include the Dexcom G7 and the Medtronic Guardian Sensor 3.

Because real-time CGMs offer constant data and proactive alerts, they are ideal for individuals who want to stay on top of their glucose trends without remembering to scan. People with a history of severe hypoglycemia or hypoglycemia unawareness often prefer rtCGMs, as the alarms can wake them during the night. The downside is that real-time sensors generally have a shorter wear time (7–10 days) and may be more expensive. However, many users find the peace of mind well worth the cost, especially when insurance covers a large portion of the expense.

Flash Glucose Monitoring Systems

Flash glucose monitors, commonly known as intermittently scanned CGMs (isCGMs), require the user to manually scan the sensor with a reader or smartphone to obtain a reading. The sensor continuously records glucose data, but that data is only displayed when you actively scan it. The most popular example is the Abbott FreeStyle Libre series, including the Libre 2 and Libre 3.

Flash systems are often cited for their affordability and ease of use. The sensor can be worn for up to 14 days (Libre 3) and does not require calibration with finger sticks. Users like that they can check their glucose as often—or as rarely—as they want, without being inundated with alerts. The trade-off is that you will not be notified of a low or high unless you happen to scan. Some newer versions of flash monitors now offer optional real-time alarms (e.g., Libre 2 with Bluetooth alerts), blurring the line between flash and real-time. Still, the core experience remains user-triggered scanning, which suits people who prefer a simpler, less intrusive system.

Professional CGMs

Professional CGMs are diagnostic tools used by healthcare providers to collect glucose data over a short period, usually 7 to 14 days. The sensor is placed on the patient in the clinic, and the patient wears it home. The device records continuous glucose levels, but the patient does not see the data in real time. After the monitoring period, the patient returns to the clinic, and the provider downloads the data to analyze glucose patterns, identify problem times, and adjust medication or lifestyle recommendations.

Professional CGMs are not intended for daily management; they are a snapshot of glucose behavior. They are especially valuable for people with type 2 diabetes who are not on insulin, or for anyone whose blood sugar control is puzzling their care team. Because the patient cannot see the readings, there is no risk of treatment decisions based on real-time data during the monitoring period. Examples include the Abbott Libre Pro and the Medtronic iPro2.

Implantable CGMs

An emerging category is the fully implantable CGM, where a small sensor is surgically inserted under the skin of the upper arm and lasts for up to 90 days. The Eversense CGM from Senseonics is the leading example. Unlike traditional CGMs that have a protruding sensor and adhesive patch, the Eversense sensor is completely inside the body. A rechargeable transmitter worn over the sensor site powers the system and sends data to a smartphone app.

Implantable CGMs offer the longest wear time and eliminate the need for weekly sensor changes. They also provide real-time data with customizable alerts. The trade-offs include a minor surgical procedure for insertion and removal, a daily 20-second warm-up after sensor insertion, and a slightly larger transmitter on the skin. Many users appreciate the discreetness and reduced skin irritation compared to adhesive-based sensors. This option is best for those who want minimal hassle with sensor changes and are comfortable with a one-time in-office procedure.

Factors to Consider When Choosing a CGM

With multiple options available, narrowing down the best CGM involves evaluating several personal and practical factors. Here are the most important considerations.

Cost and Insurance Coverage

CGM prices range from roughly $200 to $400 per month for sensors and transmitters (if not covered), and insurance coverage varies widely. Medicare now covers CGMs for beneficiaries on insulin, and many private insurers follow similar guidelines. Some plans require prior authorization, while others have preferred brands. It is critical to check with your insurance provider to see which CGMs are on your plan’s formulary. For uninsured or underinsured users, some manufacturers offer patient assistance programs. The out-of-pocket cost difference between a flash monitor and a real-time CGM can be significant, so your budget is a major driver. Always factor in the cost of replacement sensors, transmitters, and any required smartphone compatibility.

Ease of Use and Setup

Consider how comfortable you are with technology. Flash monitors like the FreeStyle Libre are straightforward: clean the skin, apply the sensor, and start scanning. Real-time CGMs may involve a calibration finger stick (some require none), pairing the transmitter via Bluetooth, and setting up alert thresholds. Some devices require a separate receiver if you do not have a compatible smartphone. If you are not tech-savvy or prefer a minimal learning curve, a flash system or a simple real-time CGM like the Dexcom G7 (which has a fully disposable, one-piece sensor/transmitter) may be easier. For caregivers managing a child’s diabetes, a real-time system with remote monitoring capabilities (shareable data on a parent’s phone) is often more practical.

Data Accuracy and Reliability

Accuracy is measured by Mean Absolute Relative Difference (MARD) — a lower MARD percentage indicates better accuracy. Current top-tier real-time CGMs have MARD values around 8–9%, while flash monitors are slightly higher (around 9–10%). Implantable CGMs like Eversense also have competitive accuracy. But accuracy is not just about the number; it is about consistency across the glucose range, especially during rapid changes. Read user reviews and consult your endocrinologist about which device has proven reliable in your glucose range. The FDA’s database of cleared CGM systems is a good starting point for understanding manufacturer claims and clinical trials.

Sensor Wear Duration

Sensor replacement frequency is a practical factor. Most real-time sensors last 7–10 days; flash sensors last 14 days; implantable sensors last up to 90 days (with a daily 20-second warm-up). Longer wear means fewer insertion events, less adhesive irritation, and less waste. However, longer-wear sensors may drift in accuracy toward the end of their life, though manufacturers have improved consistency. If you have sensitive skin or dislike the ritual of changing sensors, an implantable or 14-day flash sensor could be a better fit.

Alarms and Alerts

Real-time CGMs offer customizable alarms for urgent lows, predicted lows, high thresholds, and rate-of-change alerts. Flash monitors historically offered only low and high alarms when scanned, but newer models (Libre 3) now provide optional real-time Bluetooth alerts. Professional CGMs have no alarms. If you are prone to severe hypoglycemia or need to avoid nighttime lows, a real-time system with loud, customizable alarms is essential. Some users, however, find constant alarms disruptive; they may prefer a flash system that only notifies when they scan. Think about your personal sensitivity to alerts and whether you need to be woken up at night.

Integration with Insulin Pumps and Digital Tools

Many CGMs now integrate directly with insulin pumps to create hybrid closed-loop systems (automated insulin delivery). The Dexcom G6/G7 works with the Tandem t:slim X2 and Control-IQ technology; Medtronic’s Guardian system works with its MiniMed pumps; the FreeStyle Libre 2 and 3 integrate with the Omnipod 5 system. If you use or plan to use an insulin pump, choose a CGM that is compatible with that pump model. Integration allows the pump to automatically adjust basal insulin delivery based on CGM readings, reducing the burden of manual adjustments. Even if you are not on a pump, consider whether the CGM integrates with your preferred diabetes management apps (e.g., Apple Health, Glooko, Diasend) for data sharing with your care team.

Personal Lifestyle and Preferences

Your daily activities, sports, and work environment matter. If you swim, shower frequently, or sweat heavily, look for a CGM with strong water resistance (most are rated for submersion at 1 meter for 30 minutes or more). If you play contact sports, a smaller, low-profile sensor may stay out of the way. Implantables like Eversense have no external sensor profile beyond a thin transmitter. If you travel often, consider the availability of replacement sensors and whether the CGM app works internationally. Also, think about discretion: some people want a device that is nearly invisible under clothing, while others do not mind a visible patch. Finally, consider who else needs access to your data—parents, partners, or caregivers. Real-time CGMs with shareable data (like Dexcom Follow or LibreLinkUp) can send alerts to loved ones, which is a game-changer for peace of mind.

Making the Final Choice

No single CGM is right for everyone. The best approach is to talk with your diabetes care team, explore trial programs offered by manufacturers, and read firsthand accounts from people with similar lifestyles. Many endocrinology clinics have demo units or loaner systems so you can try before you commit. Start by identifying your top two or three priorities—whether that is cost, real-time alarms, long wear time, or pump integration—and narrow the list accordingly. Remember that the landscape is evolving rapidly; what works today may be improved or replaced by next-generation models within a year.

Investing time in choosing the right CGM now can pay off in better glucose control, fewer dangerous events, and a much easier daily routine. With the right device, you can move from reacting to your diabetes to anticipating and managing it with confidence.