The Dexcom continuous glucose monitor (CGM) reads your glucose levels every five minutes through a small sensor worn on your body, sending results to your phone or smartwatch. Getting started involves applying the sensor, pairing it with your device, setting up alerts, and learning a few practical details that make daily wear seamless. Here’s how the whole process works from start to finish.
What You Need Before You Start
The Dexcom G7 works with iPhones running iOS 18.6 or newer and Android phones running Android 13 or newer. Before applying your first sensor, download the Dexcom G7 app from your phone’s app store and create an account. You’ll also want an alcohol wipe and a clean, dry surface to work on. Each sensor box comes with the sensor inside an applicator and an overpatch for extra adhesion.
If you plan to view readings on an Apple Watch, most models from the Series 6 onward are compatible, including the Ultra and SE lines. The watch can display glucose data without your phone nearby once paired, but you’ll still need your phone the first time you connect a new sensor.
Choosing the Right Spot on Your Body
For anyone age 7 and older, the approved insertion site is the back of the upper arm. Children between 2 and 6 can also use the upper buttocks. The G7 15-Day sensor is currently approved only for adults 18 and older, placed on the back of the upper arm.
Pick an area with enough fat beneath the skin so the sensor doesn’t sit against muscle or bone. Avoid spots where clothing rubs against your waistband, where you tend to sleep on your side, or anywhere with scarring, tattoos, irritation, or heavy hair. Keep the sensor at least three inches from any insulin pump infusion set or injection site, since local blood flow changes from insulin delivery can affect accuracy.
Applying the Sensor Step by Step
Wash and dry your hands, then clean the insertion site with an alcohol wipe and let it air-dry for at least 10 seconds. Moisture under the adhesive is the most common reason sensors peel off early.
Unscrew the cap from the applicator without touching the inside. Press the applicator firmly against your skin and push the button. You’ll feel a quick pinch as a thin filament slides just under the surface. Once the sensor is in place, rub firmly around the adhesive patch three times, then press gently on the sensor body for about 10 seconds. This activates the adhesive and helps it bond to your skin.
To apply the overpatch, peel off the clear liners one at a time without touching the white adhesive. Use the colored tab to center the overpatch around the sensor, rub it down, then peel away the colored liner. The overpatch isn’t strictly required, but it significantly extends how long the sensor stays put, especially if you’re active or sweat heavily.
The Warmup Period
After insertion, the G7 needs 30 minutes to warm up before it starts displaying glucose readings. During this window the sensor is hydrating and calibrating itself against interstitial fluid beneath your skin. The older G6 model required a two-hour warmup, so the G7 is a notable improvement here.
The G7 also has a 12-hour grace period at the end of its 10-day session. When your sensor expires, you can insert a new one and delay starting it until you’re ready. This lets the new sensor settle in while the old one finishes its last hours of data, reducing or eliminating any gap in readings. It’s especially useful if you find that your sensors tend to read a bit erratically on day one.
Setting Up Alerts
Alerts are the feature that makes a CGM more than just a passive display. In the app, go to Profile, then Alerts to customize each one. The key alerts to configure are:
- High alert: Notifies you when glucose rises above a threshold you choose. Set this at the number that would actually make you take action, whether that’s correcting with insulin or going for a walk.
- Low alert: Triggers when glucose drops below your set level, giving you time to eat something before symptoms worsen.
- Urgent Low Soon: A predictive alert that warns you glucose is heading low before it gets there, often giving you a 20-minute head start.
If you’re in a meeting, at the movies, or sleeping next to a partner, you can enable Vibrate Quiet Mode, which silences all audible alerts and uses vibration only. You can set it for a fixed window of up to 6 hours or leave it on indefinitely.
Reading Your Glucose Data
The app’s main screen shows your current glucose number, a trend arrow indicating which direction it’s heading, and a graph of your recent readings. The trend arrows are just as important as the number itself. A reading of 140 mg/dL with a flat arrow means something very different from 140 with two arrows pointing straight up.
Pay attention to patterns over several days rather than reacting to every individual reading. The app stores your data and generates reports you can review with your healthcare team. You’ll start noticing how specific meals, exercise sessions, stress, and sleep affect your numbers, which is the real value of wearing a CGM continuously rather than checking with finger sticks a few times a day.
Sharing Data With Others
The Dexcom Share feature lets you send your real-time glucose data to up to 10 people. Each follower downloads the free Dexcom Follow app on their own phone. To set it up, tap the Share icon inside your Dexcom app and follow the prompts to invite followers by email. Both you and your followers need an active internet connection for data to transmit.
This feature is particularly popular among parents of children with diabetes and partners or caregivers who want to monitor glucose levels remotely. Followers can see the same glucose number, trend arrow, and alerts you see, so they can reach out or respond if something looks concerning.
Calibration and Finger Sticks
The G7 is factory-calibrated, meaning you don’t need routine finger stick calibrations to keep it accurate. This is a significant convenience improvement over older CGM generations. However, there’s one important rule: if your sensor reading doesn’t match how you feel, use a traditional blood glucose meter to make treatment decisions. A CGM reading that says 90 mg/dL when you’re shaky, sweaty, and lightheaded should not be trusted over your symptoms. Always verify with a finger stick in those moments before deciding on insulin or carbs.
Acetaminophen and Sensor Accuracy
One medication interaction worth knowing about: acetaminophen (the active ingredient in Tylenol) can affect readings if taken in large amounts. At standard doses, up to 1 gram every 6 hours for adults, the G7 remains accurate. Go above that and readings may trend falsely high. Other common pain relievers like ibuprofen don’t cause this issue, so they’re a good alternative if you need higher doses of pain relief while wearing the sensor.
Water, Sweat, and Daily Wear
The G7 sensor is waterproof to a depth of about 8 feet (2.4 meters) for up to 24 hours, so showers, baths, swimming pools, and moderate water activities are fine. You don’t need to cover or remove it. That said, prolonged hot tub soaking or high-pressure water jets aimed directly at the sensor can loosen the adhesive over time. Pat the area dry after water exposure rather than rubbing, and reapply the overpatch edges if they start peeling.
When the Sensor Has a Problem
Occasionally, your sensor may hit a snag. The most common issue is a “Brief Sensor Issue” alert, which means the sensor temporarily can’t get a glucose reading. This happens most often on the first day of a new session and typically resolves on its own within three hours. You won’t receive glucose data or alerts during this time, so keep a blood glucose meter handy as a backup. If the issue persists beyond three hours, contact Dexcom support through the app under Profile, then Contact.
A “Sensor Failed” alert is more definitive. It means the sensor can no longer function and needs to be removed and replaced with a new one. Dexcom’s support team will typically send a free replacement if a sensor fails before its expected 10-day lifespan. Save the failed sensor’s lot number (printed on the box) to speed up the replacement process.
Tips for Getting the Most Out of Your Dexcom
Rotate your insertion site each time you apply a new sensor. Using the same spot repeatedly can cause skin irritation and may reduce accuracy over time. Alternating between your left and right arm every 10 days is the simplest approach.
If adhesion is a problem, especially in hot or humid climates, applying a skin barrier wipe (like Skin-Tac) to the area before insertion can dramatically improve how well the patch sticks. Just avoid getting the product on the center of the site where the sensor filament enters the skin.
Compression lows are another common quirk. If you sleep on the arm where your sensor is placed, pressure on the sensor can temporarily push glucose readings artificially low, sometimes triggering a low alert. If you consistently get false low alarms at night, try placing the sensor on whichever arm you don’t sleep on.