Continuous Glucose Monitors: How CGMs Work and Who Benefits Most
Stuart Moore 5 January 2026 12

For people managing diabetes, checking blood sugar with a fingerstick can feel like a constant chore - mornings, meals, bedtime, and sometimes in the middle of the night. But what if you could see your glucose levels move in real time, not just as a single number, but as a story? That’s what continuous glucose monitors (CGMs) do. They don’t replace fingersticks entirely, but they give you a full picture of how your body responds to food, stress, sleep, and activity - day and night.

How Does a CGM Actually Work?

A CGM isn’t a magic box. It’s a small sensor, about the size of a coin, inserted just under your skin - usually on your belly or upper arm. Inside that sensor is a tiny filament coated with an enzyme that reacts with glucose in your interstitial fluid, the liquid surrounding your cells. When glucose interacts with that enzyme, it creates a tiny electric signal. That signal gets converted into a glucose reading.

That reading gets sent wirelessly every 1 to 5 minutes to your phone or a small receiver. Modern devices like the Dexcom G7 and FreeStyle Libre 3 don’t need you to scan them manually. They push updates automatically. The Libre 3 sends data every minute; the Dexcom G7 every five. And unlike older models, you don’t need to calibrate them with fingersticks anymore - they’re factory-calibrated and ready to go.

But here’s the catch: CGMs don’t measure blood sugar directly. They measure glucose in the fluid between your cells. That means there’s a delay - usually 5 to 20 minutes - between what’s happening in your blood and what the CGM shows. If your sugar drops fast during a run or spikes after a meal, the CGM might lag behind. That’s why you’re still told to check with a fingerstick if you feel symptoms but the CGM doesn’t match.

Who Actually Benefits from a CGM?

If you have type 1 diabetes, a CGM isn’t just helpful - it’s become standard care. The American Diabetes Association recommends them for everyone with type 1, no exceptions. Why? Because they cut severe low-blood-sugar events by 31%, according to a major 2022 study of 32 clinical trials. For parents of kids with type 1, nighttime alerts are life-changing. One user on Reddit said, “My Libre 3 alarm saved me from a 32 mg/dL hypo at 3 AM last week - I’d have been dead without it.”

People with type 2 diabetes who use insulin multiple times a day also benefit. Studies show CGMs help lower A1C by 0.5% to 0.8% - a meaningful drop that reduces long-term complications. Even if you’re not on insulin, if your blood sugar swings wildly or you’re struggling to understand how food affects you, a CGM can reveal patterns no fingerstick ever could.

And it’s not just diabetics anymore. More non-diabetic people are using CGMs to optimize energy, sleep, and metabolism. Companies like Zoe Health report an 18% annual increase in wellness users. Some athletes use them to time fueling during training. Others track how alcohol or stress spikes their sugar. While insurance won’t cover CGMs for this use yet, out-of-pocket costs are dropping.

CGM Brands Compared: Dexcom G7 vs. FreeStyle Libre 3 vs. Eversense E3

Not all CGMs are the same. Three systems dominate the market, each with different strengths.

Key Differences Between Top CGM Systems (2026)
Feature Dexcom G7 FreeStyle Libre 3 Eversense E3
Measurement Frequency Every 5 minutes Every minute Every 5 minutes
Sensor Life 10 days 14 days 180 days
Calibration Factory-calibrated Factory-calibrated Factory-calibrated
Alerts Customizable highs/lows, predictive alerts Highs/lows, but no predictive alerts Customizable, includes vibration alerts
Cost (monthly, no insurance) $399 $110 $1,200 (includes implant procedure)
Insertion Method Manual, adhesive Manual, adhesive Surgical implant
MARD Accuracy 9.1% 7.9% 8.5%

The Dexcom G7 is the most advanced in terms of alerts and integration with insulin pumps. It’s pricier but gives you early warnings before a low hits. The FreeStyle Libre 3 is the most affordable and easiest to use - no scanning needed, just wear and go. It’s the top pick for most people who want simplicity and value. The Eversense E3 is for those who hate changing sensors every two weeks. It’s implanted under the skin and lasts six months. But you need a doctor to put it in and take it out.

A family at dinner with a child's glucose trend shown as a dancing skeleton, food items transformed into sugar spikes and drops.

What You’ll See on Your Screen - And What It Really Means

It’s not just the number that matters. The real power of a CGM is in the trend arrow. A single glucose reading of 110 mg/dL could mean you’re stable, rising fast, or dropping fast. That arrow tells you the direction and speed of change.

Dr. Anne Peters, a leading diabetes expert, says, “The trend arrow showing how quickly glucose levels are changing is arguably more important than the current number itself.” If you see your sugar dropping at a rate of -3 mg/dL per minute, you know to grab a snack - even if your number is still in the normal range. If it’s rising sharply after a meal, you might adjust your insulin or take a walk.

Most apps also show daily and weekly trends. You might notice your sugar spikes every time you eat rice, or dips after evening walks. Over time, you start to predict your body’s reactions. That’s when CGMs stop being a tool and become a conversation partner with your health.

Common Problems and How to Fix Them

CGMs are reliable, but they’re not perfect. The most common complaints? Skin irritation, false alarms, and sensor failure.

Adhesive problems happen, especially with the Dexcom G6. Many users swear by Skin Tac wipes or Opsite Flexifix tape to keep sensors stuck. If your sensor falls off early, it’s usually not the device - it’s the skin prep.

False alarms are another issue. Some users report alarms during exercise, when the lag causes a mismatch between real blood sugar and the CGM reading. If you’re active and get frequent false lows, check your fingerstick before treating. Also, avoid acetaminophen (Tylenol) while using CGMs - it can interfere with readings on most devices.

Bluetooth interference is rare but real. If your Dexcom G7 stops connecting, try restarting your phone or moving away from other wireless devices. Most issues resolve within a few days as you learn how your body and device interact.

A glowing skeletal heart implant connects to a moon receiver, with sugar ghosts floating above peaceful people under a starry sky.

Cost, Insurance, and Access

Cost is the biggest barrier. Without insurance, Dexcom G7 runs about $400 a month. FreeStyle Libre 3 is half that. Eversense E3 costs more upfront but lasts longer. Insurance coverage varies wildly.

In the U.S., Medicare covers CGMs for insulin users - but only certain models. Private insurers are catching up, but many still require proof of insulin use or frequent hypoglycemia. The FreeStyle Libre 3 is now covered by Medicare for both type 1 and type 2 diabetes patients on insulin, thanks to updated guidelines in 2023.

In the UK, the NHS gives FreeStyle Libre 2 to over half a million people for free. In Canada and Australia, coverage is improving but still inconsistent. If you’re uninsured, look into manufacturer savings programs. Abbott and Dexcom both offer discount cards that can bring monthly costs down to $30-$75.

What’s Next for CGMs?

The next wave of CGMs is already here. Dexcom’s G7 has a 30-minute warm-up - down from two hours for older models. FreeStyle Libre 3 Plus now tracks insulin doses right in the app. And in 2024, Tandem’s Control-IQ 3.0 will start predicting lows 30 minutes before they happen, adjusting insulin automatically.

Non-invasive CGMs are coming too. Glucowise, a device that uses radio waves to read glucose through the skin, completed Phase 2 trials in 2023. Apple is rumored to be developing a glucose-sensing smartwatch. If it works, it could bring CGM tech to millions who’ve never considered diabetes monitoring.

Long-term, CGMs are shifting from reactive tools to proactive health guardians. A 2023 study in the New England Journal of Medicine found that CGM users had 24% fewer hospital visits for diabetes-related emergencies. That’s not just better numbers - it’s better life.

Can I use a CGM if I don’t have diabetes?

Yes, but insurance won’t cover it. Many non-diabetic people use CGMs to track how food, sleep, and stress affect their energy and metabolism. Athletes, biohackers, and people with prediabetes use them to make smarter lifestyle choices. However, interpreting the data without medical guidance can lead to unnecessary anxiety. If you’re considering it for wellness, talk to a dietitian or doctor first.

Do I still need to check my blood sugar with a fingerstick?

You still need a fingerstick in certain situations: if your CGM reading doesn’t match how you feel (like dizziness or shaking), if you’re experiencing rapid glucose changes (during exercise or illness), or if your CGM alerts you to a very low or very high reading. Fingersticks are the gold standard for accuracy - CGMs are best for trends.

How long does it take to learn how to use a CGM?

Most people get comfortable in 3 to 5 days. The biggest learning curve is understanding the trend arrows and the 5-20 minute lag. Don’t panic if your first readings seem confusing. Manufacturer apps like Dexcom Clarity and LibreView have built-in tutorials. Join online communities like r/CGM on Reddit - real users share tips that no manual can.

Are CGMs accurate during exercise?

CGMs can lag during intense activity because blood flow changes how glucose moves from blood to interstitial fluid. You might see a drop during a run that isn’t real, or a rise after a workout that’s delayed. That’s why it’s smart to check with a fingerstick before treating a low during or right after exercise. Most users adapt by learning their personal patterns - for example, knowing their sugar usually drops 15 minutes after stopping a bike ride.

Can I swim or shower with a CGM?

Yes. All modern CGMs are water-resistant and safe for showers, swimming, and sweating. Dexcom G7 and FreeStyle Libre 3 are rated for up to 1 meter of water for 30 minutes. Eversense E3 is fully implantable, so it’s waterproof indefinitely. Just avoid hot tubs or saunas for long periods - extreme heat can affect sensor accuracy.

Final Thoughts

A CGM isn’t just a gadget - it’s a way to take control. It turns guesswork into insight. It helps you sleep better, eat smarter, and avoid dangerous lows. For people with diabetes, it’s one of the most powerful tools in modern medicine. For others, it’s a window into how their body truly responds to daily life. The technology is here. The question isn’t whether you need one - it’s whether you’re ready to see what it can show you.