The Dexcom G7 is an all-in-one continuous glucose monitor that comes with the sensor and transmitter built into a single disposable applicator. You place it on the back of your upper arm, wait for a warmup period, and it sends glucose readings to your phone or smartwatch every five minutes. Here’s how the entire process works, from setup to sensor replacement.
Setting Up Your Phone or Watch
Before inserting your first sensor, you need the Dexcom G7 app installed on a compatible device. iPhones need iOS 18.6.0 or later, and Android phones need Android 13 or later. The app works with a wide range of phones from Apple, Samsung, Google, Motorola, and many other manufacturers. Dexcom recommends not updating to a brand-new operating system version until it appears on their compatibility list, since untested updates can sometimes cause connection issues.
If you want readings on your wrist without carrying your phone, the G7 supports a Direct to Watch feature on Apple Watch Series 6 or later running watchOS 10 or higher. Your iPhone still needs to be running iOS 17 or later with G7 app version 2.2.1 or newer to set this up initially, but once configured, the watch can receive readings directly from the sensor.
Choosing a Sensor Site
For anyone age 7 and older, the approved placement is the back of the upper arm. Children between ages 2 and 6 can also use the upper buttocks. The G7 15 Day sensor is only approved for the back of the upper arm in adults 18 and older.
Pick a spot with enough fat underneath to avoid pressing into muscle or bone. Avoid areas that get bumped frequently, that you lie on while sleeping, or that sit under a waistband. Stay at least 3 inches away from any insulin infusion set or injection site. Skip spots with scarring, tattoos, irritation, or heavy hair, since these can affect how well the adhesive sticks or how the sensor reads.
Inserting the Sensor
Start by washing and drying your hands. Clean the site with an alcohol wipe and let it dry completely for at least 10 seconds. Moisture under the adhesive is one of the most common reasons sensors peel off early.
Grab the applicator and unscrew the cap. Don’t touch the inside of the applicator where the sensor sits. Press the applicator firmly against your skin and push the button. You’ll feel a quick pinch as a tiny filament slides just under the surface of your skin. The sensor should rest superficially, not pressed deep. Pressing too hard during insertion increases the chance of minor bleeding at the site.
Once the sensor is in place, rub firmly around the adhesive patch three times to help it bond to your skin, then press gently on the sensor itself for about 10 seconds. The G7 comes with an overpatch for extra security. Peel off the clear liners one at a time without touching the white adhesive side, use the colored tab to position the overpatch around the sensor, rub it down, then peel off the colored liner. A mirror helps if you’re placing it on the back of your own arm.
The Warmup Period
After insertion, the sensor needs time to calibrate itself before it starts reporting glucose numbers. The standard Dexcom G7 has a 30-minute warmup. The G7 15 Day version uses a different algorithm to support its longer wear time and requires a 60-minute warmup. During this window, you won’t see any readings. The app shows a countdown timer so you know exactly when data will start flowing.
A useful trick: you can insert your new sensor before removing the old one, letting the warmup run while you’re still getting readings from the expiring sensor. This avoids any gap in your data.
Reading Your Glucose Data
Once warmup finishes, glucose readings appear on your phone or watch automatically every five minutes. The app displays your current number, a trend arrow showing which direction your glucose is heading (rising, falling, or steady), and a graph of your recent history. You can set custom high and low alerts so your phone notifies you before you actually reach a concerning level, giving you time to act.
The G7 is factory calibrated, meaning you don’t need to do routine fingerstick tests to keep it accurate. In most cases, the readings should fall within 20% of a fingerstick meter value when your glucose is 80 mg/dL or higher, or within 20 mg/dL when your glucose is below 80. If you notice the sensor consistently reads higher or lower than your meter and the difference falls outside those ranges, you can enter a manual calibration through the app. Just make sure you do it within 5 minutes of taking the fingerstick, and don’t calibrate while the app is showing a sensor error.
How Long Each Sensor Lasts
The standard Dexcom G7 sensor lasts up to 10 days. The G7 15 Day sensor lasts up to 15 days. Both versions include a 12-hour grace period after the official wear time ends, so you have some flexibility when scheduling your next sensor change. During the grace period, the sensor continues reporting readings, but you’ll get reminders that it’s time to swap.
When the session ends, peel the old sensor off your arm (pulling slowly reduces skin irritation), discard it, and start the insertion process again with a fresh applicator on a new site. Rotating between arms or shifting the placement slightly each time helps prevent skin irritation from repeated adhesive use in the same spot.
Water, Exercise, and Daily Life
The G7 is water resistant and can be submerged in up to 8 feet of water for about 24 hours. That covers showers, baths, and swimming pools without any extra protection. For extended time in water, like a long day at a water park, the overpatch helps keep the adhesive secure. Hot tubs and saunas can loosen adhesive faster than cooler water, so check the edges of your patch afterward.
During exercise, the sensor generally stays put on the back of the arm since it’s not a high-friction area. If you find the edges lifting during intense workouts or in humid weather, additional adhesive patches (sold separately by Dexcom and third-party brands) can extend the life of the bond.
Troubleshooting Common Issues
The most frequent alert you’ll see is Signal Loss, which means your phone temporarily stopped receiving data from the sensor. This usually happens when your phone is too far from the sensor (Bluetooth range is roughly 20 feet) or when something disrupts the Bluetooth connection. Moving your phone closer or toggling Bluetooth off and back on typically resolves it. If you see a “Bluetooth is off” alert, check both your phone’s system Bluetooth settings and the in-app Bluetooth toggle.
If you enter a fingerstick calibration and the app shows “Calibration Not Used,” it means the sensor couldn’t incorporate that value. This can happen if the calibration was entered during rapid glucose changes or if the value was far outside what the sensor expected. Wait until your glucose is relatively stable and try again.
Sensor failures before the expected wear period ends do happen occasionally. If your sensor stops working early, contact Dexcom technical support as soon as possible. They typically send a free replacement sensor for confirmed early failures.
Minor bleeding at the insertion site is uncommon but not dangerous. It usually means the filament nicked a small capillary. A small amount of blood under the adhesive patch generally doesn’t affect readings, but heavy bleeding or persistent pain may mean the sensor should be removed and a new one placed at a different site.