The Dexcom G7 is a continuous glucose monitor (CGM) that measures glucose in the interstitial fluid just below the skin every 5 minutes and streams the readings to your phone or a Dexcom receiver over Bluetooth. Each sensor is a small all-in-one disposable device that wears for up to 10 days plus a 12-hour grace period, with a 30-minute warm-up after insertion and no fingerstick calibration required.
The Sensor Itself
The G7 sensor is about the size of a stack of four quarters and weighs a fraction of an ounce. Inside the disposable body are three key components:
- A flexible metal filament about the width of a human hair, coated with glucose oxidase enzyme and platinum electrodes, that sits a few millimeters below the skin
- Electronics that power the electrochemical reaction, read the resulting current, and apply calibration algorithms
- A Bluetooth Low Energy radio that transmits readings to nearby devices
- A small lithium battery sized to last the 10-day wear period
Everything is sealed in a water-resistant (IP28, submersible to 8 feet for 24 hours) adhesive patch.
How the Filament Actually Senses Glucose
The metal filament is coated with glucose oxidase, an enzyme that reacts with glucose molecules to produce hydrogen peroxide. The peroxide is oxidized at the electrode surface, releasing electrons. The resulting small electrical current is proportional to glucose concentration in the interstitial fluid around the filament. The sensor reads this current every 5 minutes, applies factory calibration plus temperature compensation, and reports a plasma-equivalent glucose value.
Why Interstitial Glucose, Not Blood Glucose
Interstitial fluid is the thin layer of fluid between cells. Glucose moves from the bloodstream into this fluid through capillary walls. When blood glucose rises after a meal, interstitial glucose rises a few minutes later. When blood glucose falls (for example during a hypoglycemic event), interstitial glucose falls a few minutes later. This 5-to-15 minute lag is why a CGM reading during rapid change can differ from a simultaneous fingerstick; during stable glucose, the two track within about 10 percent.
What Happens From Sensor to Phone
- Every 5 minutes, the sensor electronics sample the current from the filament.
- Algorithms apply factory calibration and temperature correction to produce a glucose value in mg/dL or mmol/L.
- The value is time-stamped and stored in the sensor’s memory.
- The Bluetooth Low Energy radio broadcasts the value to paired devices within about 20 feet.
- The Dexcom G7 app on your phone or the Dexcom receiver receives the packet, updates the graph, and evaluates alert thresholds.
- If a threshold is crossed (low, high, rapid change), the app or receiver sounds an alert and sends a push notification.
- The app uploads data to Dexcom’s cloud (Clarity) for trend analysis and clinician sharing, if the user opts in.
Wear Time, Warm-Up, and Grace Period
| Phase | Duration | What Happens |
|---|---|---|
| Insertion | One-button press | Applicator inserts the filament with a hidden needle; the needle retracts and is discarded |
| Warm-up | 30 minutes | No glucose readings displayed; sensor is stabilizing in tissue |
| Active wear | 10 days | Glucose reading every 5 minutes; all alerts active |
| Grace period | 12 hours after 10 days | Sensor continues to work; app reminds you to replace |
| Expiration | After grace period | Sensor stops transmitting; replace with a new one |
Accuracy: What MARD Means
CGM accuracy is typically reported as median absolute relative difference (MARD) compared with a lab reference. The Dexcom G7’s MARD is roughly 8 to 9 percent in registration trials — excellent for any CGM. In plain terms, if lab glucose is 100 mg/dL, most G7 readings fall between 91 and 109 mg/dL. Accuracy is slightly lower in the first 12 to 24 hours after insertion (tissue adaptation period) and in the extreme high (above 300) and very low (below 60) ranges.
Bluetooth Range and Connectivity
- Up to 20 feet (6 meters) line-of-sight to your phone or receiver
- Walls, dense furniture, and water reduce effective range
- If you move out of range, the sensor stores readings and fills in the gap when you reconnect, as long as the outage is under 3 hours
- The sensor can stream to your phone, the Dexcom receiver, and certain insulin pumps (Tandem t:slim X2, Tandem Mobi, Omnipod 5) at the same time
- The Dexcom Follow app lets up to 10 caregivers or family members see your readings remotely with your permission
Alerts You Can Configure
- Low glucose alert (default 80 mg/dL; adjustable 60 to 100)
- High glucose alert (default 200 mg/dL; adjustable 120 to 400)
- Urgent low alarm (fixed at 55 mg/dL; cannot be disabled — safety feature)
- Rate of change alerts (rapid rise or fall)
- Signal loss notification
- Sensor expiration reminders
What You Can Do With the Data
- Watch post-meal curves to learn which foods spike you and by how much
- Time exercise to flatten post-meal glucose
- Adjust insulin dosing with your prescriber based on patterns, not guesses
- Share readings with family or caregivers through Dexcom Follow
- Upload to Dexcom Clarity for long-term trend analysis
- Integrate with Tandem pumps, Omnipod 5, and third-party apps via API
Limitations
- Not designed to replace fingersticks during severe, rapid glucose changes or in shock states
- Accuracy is lower in the first 12 to 24 hours after insertion
- Acetaminophen at normal doses does not interfere (improvement over older CGMs), but hydroxyurea can falsely raise readings
- Sensor adhesive failures do occur; tape or overpatches help
- MRI, CT with contrast, and certain medical procedures require sensor removal
Related Reading
See our companion guides on the G7 all-in-one design, the G7 receiver, GMI on Dexcom G7, and the broader detection of prediabetes hub.
The Bottom Line
The Dexcom G7 works by placing a tiny enzyme-coated filament just under the skin, reading a small electrical current that tracks glucose concentration in interstitial fluid, and sending a reading every 5 minutes over Bluetooth to your phone or receiver. Wear time is 10 days plus a 12-hour grace period, warm-up is 30 minutes, accuracy is around 8 to 9 percent MARD, and data can be shared with family and clinicians. Once you understand the mechanism — a continuous stream of interstitial glucose measurements — the G7’s capabilities and its few limitations both make more sense.
