Using a Dexcom continuous glucose monitor involves applying a small sensor to your skin, pairing it with your phone or receiver, and then reading real-time glucose data throughout the day without routine fingersticks. The process is straightforward once you understand the basics of sensor application, placement, and what your readings mean. Here’s how it all works, whether you’re using a G7 or the newer G7 15 Day sensor.
Choosing a Sensor Site
The back of your upper arm is the primary approved location for anyone age 2 and older. For young children between ages 2 and 6, the upper buttocks is also an option. The G7 15 Day sensor is currently approved only for the back of the upper arm in adults 18 and older.
Pick a spot with some natural padding. Avoid placing the sensor directly over bone, on irritated or scarred skin, over tattoos, or anywhere that gets bumped frequently (like where a seatbelt sits or a bag strap rubs). If you rotate between your left and right arm with each new sensor, you give each site time to recover.
Preparing Your Skin
Good skin prep is the single biggest factor in whether your sensor stays on for the full wear period. Start by washing the area with an oil-free soap and drying it completely. Wipe the spot with an alcohol swab and let it air dry before you do anything else. Don’t apply the sensor right after a shower or in a humid bathroom, because moisture trapped under the adhesive loosens it faster. If you tend to have oily skin, gentle exfoliation beforehand helps. If the area is hairy, trim it with a dry razor first.
Skip any lotions, oils, or moisturizers on or near the insertion site. If you sweat heavily, applying unscented antiperspirant in an oval shape around (not on) the exact spot where the sensor will sit can help. Let it dry for 10 to 15 minutes, then place the sensor on the clean skin in the center of that oval.
Inserting the Sensor
The G7 uses an all-in-one applicator that contains both the sensor and transmitter in a single disposable unit, which is 60% smaller than the older G6 design. There’s no separate transmitter to snap in.
Wash and dry your hands. Unscrew the cap from the applicator, being careful not to touch the inside. Place the flat end of the applicator firmly against your prepared skin site. Press the button on the applicator. You’ll feel a quick pinch as a thin, flexible filament slides just under your skin. This filament is what measures glucose in your interstitial fluid. Pull the applicator straight away. The sensor patch stays behind, stuck flat against your skin. Dispose of the applicator according to your local guidelines for items that have contacted blood.
The entire process takes about 30 seconds once you’ve prepped the site.
Pairing With Your Phone
You’ll need the Dexcom app installed on a compatible device. The G7 app requires at least iOS 18.6 for iPhones or Android 13 for Android phones. Compatible Android brands include Samsung, Google Pixel, Motorola, OnePlus, Sony, Xiaomi, and many others. Check Dexcom’s compatibility page if you’re unsure about your specific model.
Open the app and follow the on-screen pairing prompts after inserting your sensor. The G7 connects via Bluetooth, so keep your phone within about 20 feet of the sensor for a reliable connection. Once paired, the sensor enters a 30-minute warmup period. During this time, the sensor is hydrating and calibrating itself under your skin. After those 30 minutes, glucose readings start appearing automatically. The older G6, by comparison, required a 2-hour warmup.
How Long Each Sensor Lasts
The standard G7 sensor lasts up to 10 days. The G7 15 Day sensor, as the name suggests, lasts up to 15 days. Both versions include a 12-hour grace period at the end of the session, so you don’t have to swap sensors at an inconvenient time. You’ll get a notification as your session nears its end, giving you time to have a replacement ready. When the session expires (including the grace period), the sensor stops transmitting and you remove it by peeling the adhesive patch off your skin.
Reading Your Glucose Data
The app displays your current glucose number and a trend arrow showing which direction your levels are heading. These arrows are the most actionable part of the system.
- Steady arrow (flat or slightly angled): Your glucose is changing slowly, less than about 1 mg/dL per minute. No immediate action needed.
- Single arrow up or down: Your glucose is rising or falling at a moderate pace, roughly 1 to 2 mg/dL per minute.
- Double arrow up or down: Your glucose is changing rapidly, more than 2 mg/dL per minute. This means your actual glucose could be significantly different in just 15 to 20 minutes.
The trend arrows matter because your current number is a snapshot, but the arrow tells you where you’re heading. A reading of 130 mg/dL with a double arrow pointing down is a very different situation than 130 mg/dL holding steady.
The Dexcom system is factory-calibrated, so you don’t need to do routine fingerstick calibrations. However, if your sensor reading doesn’t match how you feel (for example, the app shows a normal number but you feel shaky or lightheaded), use a traditional blood glucose meter to confirm and make treatment decisions based on that fingerstick instead.
Keeping the Sensor Stuck
Active lifestyles, sweating, and showers can loosen adhesive over a 10 or 15 day wear period. If your sensors tend to peel early, you have a few options. Dexcom provides free overpatches that stick on top of the sensor to hold it down. You can also use medical adhesive films like Tegaderm or IV3000, placed over the sensor tape as reinforcement.
For a barrier approach (protecting sensitive skin while still keeping things secure), place a thin medical bandage or patch on your skin first, cut an oval-shaped hole in the center, then insert the sensor through that hole onto bare skin. The adhesive grips the bandage instead of your skin directly, while the sensor filament still contacts your body. If you use a barrier film product, let it dry completely before applying the sensor on top.
Troubleshooting Common Alerts
Signal Loss and No Readings
Both of these mean your phone isn’t getting data from the sensor, but for different reasons. “No Readings” usually means something is physically blocking the Bluetooth signal. Water trapped between the sensor and your phone, a wall between you and your device, or even lying directly on top of the sensor while sleeping can cause it. Move your phone closer and wait about 10 minutes.
“Signal Loss” can happen if your phone is too far away, if your phone’s operating system has a bug affecting Bluetooth, or occasionally if the transmitter isn’t functioning properly. While you’re waiting for the signal to return, use a fingerstick meter for any treatment decisions.
Sensor Error
A sensor error is different. Your transmitter is still communicating with your phone, but the sensor itself can’t determine an accurate glucose value. This can happen if the sensor filament has partially pulled out, or if unusual physiological conditions are interfering with the reading. If the sensor can’t recover, you’ll need to replace it. The good news: only the sensor needs replacing, not any other hardware. Dexcom’s support team will typically send a free replacement if a sensor fails before its expected wear period ends.
Tips for the First Few Days
Sensor accuracy tends to improve after the first 12 to 24 hours as the filament fully settles into the tissue. Some people notice slightly less reliable readings on day one compared to the rest of the session. This is normal and doesn’t mean the sensor is faulty.
You can shower, swim, and exercise with the sensor on. It’s water-resistant for brief submersion, though prolonged soaking (like a long bath) can weaken the adhesive over time. Pat the sensor area dry afterward rather than rubbing it. If you’re new to CGM, the sheer volume of data can feel overwhelming at first. Focus on the trend arrows and your time in range rather than reacting to every individual number. Patterns over hours and days tell you far more than any single reading.