Dexcom sensors are small wearable devices that measure glucose in the interstitial fluid under your skin and send readings to a phone or receiver in near real time. The current lineup includes the prescription Dexcom G6 and G7 systems used for people with diabetes and the over-the-counter Dexcom Stelo used by adults who do not take insulin. All three are FDA-cleared and share similar underlying sensor technology.
How a Dexcom Sensor Actually Measures Glucose
Each Dexcom sensor has a thin flexible wire, typically about a third of an inch long, that sits in the layer of fluid surrounding cells just under the skin. That interstitial fluid contains glucose in concentrations that track closely with blood glucose, though with a short delay of several minutes during rapid rises or falls. The sensor wire is coated with an enzyme, glucose oxidase, which reacts with glucose and generates a tiny electrical current proportional to the glucose concentration. The sensor module converts that current into a reading and transmits it to a phone app via Bluetooth.
The G7 transmits a new reading every minute; the G6 every five minutes. Data is smoothed and presented with trend arrows that indicate whether glucose is stable, rising, or falling and how fast. These arrows are often more useful than any single number because they help anticipate a low or a high before it arrives.
Comparing the Dexcom Sensor Lineup
The three currently active Dexcom sensors share a core measurement approach but differ in size, wear time, indication, and app features. The table below outlines the main differences as of the FDA clearances at the time of writing.
| Sensor | Prescription status | Wear time | Primary indication | App features |
|---|---|---|---|---|
| Dexcom G6 | Prescription | 10 days | Ages 2+, insulin users supported | Alerts, Share, Clarity, pump integration |
| Dexcom G7 | Prescription | 10 days plus 12-hour grace | Ages 2+, pregnancy, insulin users | Faster warm-up, smaller sensor, direct-to-watch |
| Dexcom Stelo | Over the counter | Up to 15 days | Adults 18+ not using insulin | Spike alerts, trend summary, no insulin dosing |
Accuracy and What It Means in Practice
CGM accuracy is reported as mean absolute relative difference (MARD). G7 has pivotal trial MARD near 8 percent in adults, among the most accurate CGMs cleared by the FDA. G6 MARD is about 9 percent. These numbers come from the pivotal studies submitted in the FDA clearance files. A MARD of 8 to 9 percent means that, on average, CGM readings are within that percentage of a lab reference value across the day.
Individual results depend on many factors: sensor site, pressure during sleep, hydration, and how recently the sensor was inserted. Compression lows, which occur when you sleep on the sensor, can cause a temporarily low reading that resolves when you change position. The 12-hour warm-up readings on G6 or 30-minute warm-up on G7 are normal.
Where to Place the Sensor
Dexcom G7 is FDA-cleared for the back of the upper arm and the upper buttocks in children aged 2 to 6. G6 is labeled for the abdomen in adults and the upper buttocks in pediatric users. Clean skin with soap and water, dry fully, and avoid areas with scars, tattoos, or recent insulin injection sites.
For broader context on blood sugar monitoring, readers can review our prediabetes overview, which explains when CGMs are useful even before diabetes is diagnosed, and our A1C levels guide, which complements the minute-to-minute picture with a three-month average.
Who Should Use Which Dexcom Sensor
People with type 1 diabetes, insulin-using type 2 diabetes, or pregnancy in women with diabetes typically benefit most from G7, which is the newest prescription sensor and integrates with insulin pumps and smart pens. G6 remains in use where pump compatibility or personal preference favors it, and for patients whose insurance plans cover only G6. Stelo is appropriate for adults with prediabetes or type 2 diabetes on non-insulin therapy who want glucose insights without a prescription.
For people exploring treatment options, our treatment hub outlines how CGM data often supports lifestyle and medication decisions in a structured care plan.
Tips to Get the Most From a Dexcom Sensor
- Stick to recommended sites and rotate with each new sensor.
- Use an overpatch if you exercise heavily or live in a humid climate.
- Give the sensor its full warm-up period before expecting accurate readings.
- Pair readings with food and activity notes to see patterns.
- Export Clarity reports or app summaries for your clinician visits.
Regulatory and Clinical Context
Dexcom sensors are cleared under the FDA’s integrated continuous glucose monitor framework, which allows data to flow into approved insulin pumps and decision-support tools. The FDA G7 clearance summary and the Stelo De Novo decision describe the accuracy requirements and intended use in detail. The American Diabetes Association’s annual Standards of Care recommend CGM for most people on insulin and increasingly for people on non-insulin therapies who are at risk of hypoglycemia or poor control.
The Bottom Line
Dexcom sensors use a tiny under-the-skin wire to measure glucose continuously, with the G6 and G7 requiring a prescription and Stelo available over the counter for adults who do not use insulin. All three are FDA-cleared with MARDs in the high single digits. Choosing the right sensor depends on whether you need insulin dosing support, your wear-time preferences, and how you plan to use the data. Your clinician can help confirm which system fits your situation best.
Medical disclaimer: This article is for educational purposes only and is not a substitute for advice from a qualified healthcare professional. Discuss any changes in monitoring or treatment with your clinician.
