Last reviewed August 21, 2026 by the Medically Modern coverage team. Specifications come from Dexcom’s US product documentation. Always follow the instructions supplied with your own sensors.
A Dexcom G7® sensor is one disposable unit containing the glucose-sensing filament, the electronics, and the transmitter that talks to your phone. You wear it, it expires, you throw the whole thing away and open a new one.
That is a change from the Dexcom G6, which used a sensor plus a separate reusable transmitter you unclipped and carried from one sensor to the next. Nothing to transfer on the G7, and nothing to lose. The trade-off is that the transmitter is no longer reusable, so the disposable is doing more work.
If you want the wider picture of what the system does rather than the hardware, start with what the Dexcom G7 is. This page is about the piece on your arm.
Size and what is under the adhesive
The G7 sensor is roughly 24 × 27.3 × 4.6 mm and about 60% smaller than the G6 sensor it replaced. In practice that is a small oval slightly larger than a US quarter and about as thick as three stacked quarters.
The part that goes under your skin is a flexible filament a few millimeters long, not a needle. The applicator inserts it and withdraws in one motion. Nothing rigid stays in your arm, which is why most people stop noticing the sensor within an hour of putting it on.
Where to wear it
Approved sites depend on age, and they are not interchangeable.
| Site | Approved for | Notes |
|---|---|---|
| Back of the upper arm | Ages 2 and older | The default. Measured more accurate than the abdomen in Dexcom’s study. |
| Upper buttocks | Children aged 2–6 only | Practical for small children who would knock an arm sensor. |
| Abdomen | Adults only | Approved, but the accuracy figures were slightly worse than arm placement. |
Two practical points that the approved-site list does not tell you.
First, rotate. Using the same square inch of skin every time builds up scar tissue, and scarred tissue reads worse. Alternate arms at minimum.
Second, think about how you sleep. Pressure on a sensor restricts blood flow around the filament and can produce a false low reading in the middle of the night. If you sleep on your left side, a sensor on your left arm will get compressed. This is common enough to have a name — a compression low — and it is covered on the accuracy page.
Applying one
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Pick and clean the site
Choose a spot away from bone, scarring, and anywhere a waistband or bra strap sits. Wash with soap and water, then wipe with alcohol and let it dry completely. Adhesive does not stick to damp or oily skin, and most sensors that fall off early failed at this step.
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Apply the sensor
Peel the adhesive liner, place the applicator flat against your skin, and press the button. Insertion is one motion and takes about a second. Most people report a brief pinch or nothing.
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Pair it with your phone or receiver
The app scans the pairing code on the applicator or the sensor box. Keep the box until pairing succeeds, since the code is on it.
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Wait out the warm-up
30 minutes for a standard G7. 60 minutes for a G7 15 Day, which runs a different algorithm to support the longer wear. No readings appear during warm-up. Plan the change for a stretch when you are not about to eat or drive.
Change sensors in the morning, not at bedtime. A sensor started at 9pm spends its warm-up while you are asleep, and the first hours of a new sensor are the least settled. Starting in the morning means the shakiest period happens while you are awake to notice it.
How long one lasts
| Dexcom G7 | Dexcom G7 15 Day | |
|---|---|---|
| Wear period | Up to 10 days | Up to 15 days |
| Grace period | 12 hours | 12 hours |
| Warm-up | 30 minutes | 60 minutes |
| Sensors per 30 days | 3 | 2 |
| Ages | 2 and older | 18 and older |
The 12-hour grace period runs after the official end of wear. Readings continue during it, so a sensor expiring at 2am does not force a 2am change. It is a buffer, not bonus wear time — do not plan around using it every cycle.
The sensors-per-month figures are what your supply should look like: three boxes-worth per 30 days on the standard sensor, two on the 15 Day. If your pharmacy or supplier is sending a different quantity, something is wrong with how the order was written.
Water, exercise, and keeping it attached
Dexcom states the sensor may be submerged to about 8 feet of water for up to 24 hours when properly applied. Showers, baths, pools, and the ocean are all fine. The optional receiver is not waterproof, so that stays on dry land.
Staying attached for the full wear is a different problem from being waterproof. Things that help:
- Let the skin dry fully before applying. The single biggest factor.
- Press for a few seconds after application so body heat sets the adhesive.
- Use an overpatch if you swim, sweat heavily, or work with your hands overhead. These are sold separately by several manufacturers and go over the sensor without covering the electronics.
- Pat dry rather than rubbing with a towel, which is how a lot of sensors get caught and peeled.
Not sure what your sensors would cost?
We check your benefits with your insurer and tell you the monthly number before anything ships.
When a sensor fails early
Sensors do fail before their time. In the clearance study for the 15 Day sensor, 73.9% lasted the full 15 days — which means roughly one in four did not. That is a published figure from Dexcom’s own trial, not a complaint.
Dexcom replaces sensors that fail prematurely, but you have to ask. Replacement is not automatic and nobody will notice on your behalf. Before you call:
- Note the sensor serial number (in the app, and on the box).
- Note when it was applied and when it failed, and what the app displayed.
- Keep the sensor if you can — Dexcom occasionally asks for it back.
Dexcom technical support handles these at 1-888-738-3646. If you get your supplies through Medically Modern, tell us as well and we will help chase it.
A sensor reading oddly is not always a failed sensor. Pressure on the site, the first hours after insertion, and certain medications all produce readings that look wrong but come from a working sensor. Check the accuracy page before assuming hardware is the problem, and confirm with a fingerstick if a reading does not match how you feel.
Taking one off
Peel the adhesive edge slowly rather than pulling the sensor straight off. An adhesive remover wipe, or a little baby oil worked around the edge, makes it painless and saves your skin over months of changes. The whole unit goes in the bin — there is no transmitter to keep.
If the adhesive leaves your skin red or itchy at every change, a barrier wipe applied before the sensor can help. Persistent reactions are worth raising with your clinician rather than living with.
Frequently asked questions
Can you reuse a Dexcom G7 sensor?
No. The transmitter is built into the sensor and the unit is designed for a single wear. Once removed, a sensor cannot be reapplied — the adhesive and the filament are both single-use.
Can you shower and swim with a Dexcom G7 sensor?
Yes. Dexcom states the sensor may be submerged to about 8 feet for up to 24 hours when correctly applied. Keep the receiver away from water, since it has no such rating.
Why is there no reading during warm-up?
The filament needs time to settle into the interstitial fluid before its output is reliable. Standard G7 takes 30 minutes; the G7 15 Day takes 60 minutes because of the algorithm supporting its longer wear. Use a fingerstick meter during that window if you need a number.
Can you wear a Dexcom G7 sensor on your thigh?
The thigh is not an approved site in the US. Approved placements are the back of the upper arm (ages 2+), the upper buttocks (ages 2–6), and the abdomen (adults). Using an unapproved site means the accuracy data no longer applies to your readings.
Does the sensor keep working if your phone is away?
The sensor keeps measuring, but readings only reach the app when the phone is in Bluetooth range. Once reconnected the app backfills missed readings. Alerts do not fire while you are out of range, which matters overnight if the phone charges in another room.
Sources: Dexcom sensor wear time, Dexcom G7 15 Day warm-up, Dexcom water resistance, Dexcom G7 overview, Garg et al., accuracy and safety of the Dexcom G7 (PubMed), Garg et al., accuracy of the 15.5-day G7 iCGM (PubMed).