Updated April 2026 by Susie Adriance, CFO of Peak Medical Supplies. Reviewed for plain-English clarity and Medicare accuracy.
If you or your spouse just got handed a CGM prescription and you’re asking, “What even IS this thing?” — you’re exactly who I wrote this for.
A CGM, or continuous glucose monitor, is a small sensor you wear on the back of your arm that checks your blood sugar around the clock. No fingersticks. No waking up at 3 a.m. to poke yourself. It sends readings to your phone (or to a little handheld reader) every few minutes, all day and all night.
I’ve spent over ten years in the durable medical equipment (DME) business helping Medicare seniors get these devices. I’m not a doctor — your doctor is your doctor — but I know this paperwork and this technology inside and out. My goal here is simple: by the end of this page, you’ll understand what a CGM is, how it works, and whether it makes sense for you.
Here’s what we’ll cover:
- What a CGM actually is (one paragraph, no jargon)
- How it works, step by step
- How it compares to the old fingerstick way
- The science, in three short paragraphs
- Who qualifies on Medicare
- The three CGMs seniors actually use
- What CGMs don’t do
- Real questions my customers ask me
- Your next step
What a CGM Actually Is
A CGM is a wearable sensor about the size of two stacked quarters. It sticks to the back of your upper arm with medical adhesive and stays there for 10 to 15 days, depending on the brand.
Under that little round patch is a tiny, flexible filament — thinner than a hair — that sits just under the skin. It measures the sugar in the fluid between your cells (we’ll get to that in a minute). Every one to five minutes, it sends a fresh reading to your phone or reader.
At the end of the sensor’s wear time, you peel the old one off and stick a new one on. That’s it. That’s the whole device.
How a CGM Works — Step by Step
Here’s exactly what happens from the box to a live reading on your phone.
Step 1: You put the sensor on
The sensor comes in a single-use applicator — basically a plastic cup. You twist off the cap, press the applicator against the back of your arm, and push the button. It clicks. You feel a tap. Done.
The whole thing takes about three seconds. Most of my customers tell me it’s less uncomfortable than getting a flu shot. A lot of folks don’t feel it at all.
There is a tiny, bendable filament that goes under your skin — but there’s no visible needle sticking out and you can’t feel it once it’s in.
Step 2: The sensor warms up
Once the sensor is on, it needs to “warm up” before it shows readings. This takes about 60 minutes (FreeStyle Libre 3) or 30 minutes (Dexcom G7). You can go about your day normally during this time.
Step 3: Continuous readings every few minutes
After warm-up, you’ll see a blood sugar number on your phone or reader. It updates on its own — every one minute for FreeStyle Libre 3, every five minutes for Dexcom G7.
You don’t have to do anything. No button to press. No poking. It just keeps measuring.
Step 4: The data lands on your phone (or a handheld reader)
Most people use a smartphone app to see their numbers. If you don’t have a smartphone — and plenty of my customers don’t — both major brands make a separate handheld device called a “reader” that does the same job.
The screen shows three things: your current number, a little arrow pointing up, down, or sideways, and a graph of your day. More on those arrows in a minute — they’re the reason doctors love these devices.
Step 5: You change the sensor every 10–15 days
When the sensor reaches the end of its life, the app lets you know a day or two ahead. You peel the old one off (it comes off like a Band-Aid), toss it, and apply a new one. Your readings pick up right where they left off.
CGM vs. the Old Fingerstick — What Actually Changes
If you’ve been checking your blood sugar the traditional way, you know the routine: prick your finger, squeeze out a drop, touch it to a test strip, wait for the meter to beep. Maybe four times a day if you’re diligent.
Here’s what changes when you switch to a CGM:
| Fingerstick | CGM |
|---|---|
| 4 readings a day (if you’re faithful) | 288+ readings a day, automatically |
| Hurts a little every time | One painless application every 10–15 days |
| You see a number — no trend | You see a number and whether it’s rising or falling |
| No alerts | Phone alarms for highs and lows |
| No data while you sleep | Tracks overnight — catches silent lows |
That trend arrow is the killer feature. A number of 110 with an arrow pointing straight up is very different from 110 with an arrow pointing down. One means you’re heading for a high; the other means you’re about to drop. The old fingerstick can’t tell you which way you’re going.
Why this matters more after 65: Low blood sugar is especially risky for older adults. It can cause falls, confusion, and in rare cases serious heart events. An alarm on your phone when you’re trending low — especially at night — is a genuine safety feature, not a gadget.
The Science, in Three Short Paragraphs
1. It measures interstitial fluid, not blood. A CGM doesn’t actually dip into your bloodstream. It measures sugar in the fluid between your cells, which is called interstitial fluid. Blood sugar shows up there too — just a few minutes later. That’s why CGM readings can lag behind a fingerstick by about 5 to 15 minutes, especially when your blood sugar is changing fast.
2. It uses a tiny enzyme and an electrical signal. On the tip of that thin filament is a coating that reacts with glucose. That reaction creates a very small electrical current. The sensor reads the current, converts it to a number, and sends it to your phone. No blood draw, no lab.
3. It’s FDA-cleared and accurate enough to make decisions. Modern CGMs are approved by the FDA to replace most fingersticks for treatment decisions. Accuracy is measured with something called MARD (Mean Absolute Relative Difference) — the lower, the better. Today’s top CGMs land in the 7–9% range, which is considered clinically accurate for everyday diabetes management.
Who Qualifies for a CGM on Medicare?
Medicare Part B covers CGMs for most people with diabetes — a much broader group than it used to. As of 2026, the rules are meaningfully simpler than they were a few years ago.
Here’s the short version of who qualifies:
- You’re enrolled in Medicare Part B
- You have a diagnosis of diabetes (Type 1 or Type 2)
- You use insulin of any kind — OR you’ve had documented low-blood-sugar episodes (called “problematic hypoglycemia”)
- You see your doctor every 6 months to review how you’re doing
That’s the plain-English version. There are details, and the paperwork matters — a denial usually comes down to a missing chart note, not a patient being ineligible.
For the full walkthrough, I’ve written a detailed guide here: Medicare CGM Coverage: Complete Guide for Seniors. And if you want to see the exact Part B requirements, see Medicare Part B CGM Requirements.
Which CGM? The Three Seniors Actually Use
There are three CGMs Medicare seniors run into most often. I’ll be straight with you: Peak Medical Supplies has a direct pricing relationship with Abbott (the maker of FreeStyle Libre), and I could tell you that’s the only one worth using. I’m not going to, because that wouldn’t be honest. Here’s the real picture.
FreeStyle Libre 3 (Abbott)
- Smallest of the three — about the size of two stacked quarters
- 14-day wear time
- Reading every 1 minute
- Phone app or handheld reader available
- Generally the lowest out-of-pocket cost under Medicare Part B
More details: Does Medicare Cover FreeStyle Libre 3?
Dexcom G7
- Slightly larger sensor, 10-day wear time (plus a 12-hour grace period)
- Reading every 5 minutes
- Phone app or Dexcom receiver
- Works with certain insulin pumps if you ever move to one
- Strong choice if you want seamless integration with Apple Watch or a pump
Stelo (Dexcom, over-the-counter)
- Available without a prescription
- Aimed at people with Type 2 diabetes who aren’t on insulin
- Not covered by Medicare — it’s an out-of-pocket, retail product
- Can be a useful “try before you commit” option, but if you qualify for a prescription CGM through Medicare, that’s usually the better route
Which one is right for you depends on your routine, your phone (or lack of one), and what your doctor recommends. None of these are bad choices.
What CGMs Don’t Do
Let’s be honest about what you’re not getting. A CGM is a powerful tool, but it’s not magic.
- It doesn’t replace your doctor. Your CGM shows your numbers. Your doctor interprets them and adjusts your plan.
- It doesn’t give medical advice. Alerts are useful, but what you do about a high or a low is between you and your care team.
- It doesn’t work during MRI, CT, or X-ray scans. You’ll need to remove it first — and the sensor can’t be reused, so you’ll apply a new one after the scan.
- Its readings can differ from a fingerstick. That’s normal. Because a CGM measures interstitial fluid, a reading 5–15 minutes behind your actual blood level is expected, especially when your sugar is changing quickly.
- It doesn’t cure or treat diabetes. It’s a measuring tool — a very good one — not a treatment.
Common Questions Seniors Actually Ask Me
Does it hurt?
Almost never. The applicator clicks like a small tap on your arm. Most people feel pressure, not pain. Once it’s on, you stop noticing it within a day.
Can I shower, swim, or take a bath with it?
Yes. Both FreeStyle Libre 3 and Dexcom G7 are water-resistant and are rated for showers, baths, and swimming. Hot tubs and long soaks are the main situations where the adhesive can loosen — a waterproof patch cover helps.
What if it falls off early?
Call the manufacturer. Abbott and Dexcom both have customer service lines that will often send a free replacement sensor if one fails or falls off before its wear time is up. Keep the packaging — they’ll ask for the lot number.
How accurate is it?
Very accurate for making everyday decisions. The top CGMs have a MARD (a standard accuracy measurement) of around 8–9%, which the FDA considers accurate enough to replace most fingersticks. For confirming a treatment decision during a suspected low, your doctor may still recommend a fingerstick backup.
Can I drive with one?
Absolutely. In fact, many drivers find it safer — the low-glucose alarm can alert you to a drop before it affects your concentration. Check your number before you start the car, and keep fast-acting sugar (juice, glucose tabs) within reach, just like you always should.
Will Medicare cover it?
In most cases, yes — if you have a diabetes diagnosis and either use insulin or have documented hypoglycemia. Full walkthrough: Medicare CGM Coverage: Complete Guide for Seniors.
What if I don’t have a smartphone?
You’re not stuck. Both Abbott and Dexcom sell a separate handheld “reader” device that shows your numbers without needing a phone. Ask your DME supplier specifically for a reader when you place your order — some suppliers default to the phone-only option.
How do I actually get one prescribed?
Talk to the doctor who manages your diabetes. Ask, “Do I qualify for a continuous glucose monitor?” If yes, they’ll send a prescription to a DME supplier that handles your Medicare paperwork. That’s the short version. The longer version is below.
How to Get Started — Your Next Step
If you’ve read this far, you probably know whether a CGM sounds right for you or your loved one. Here’s the path most of my customers actually take.
- Talk to your doctor. Say, “I’d like to try a continuous glucose monitor. Do I qualify?” Bring a list of your medications and any recent low-blood-sugar episodes.
- Get the prescription sent to a DME supplier. Any Medicare-enrolled DME can fulfill it — Peak Medical Supplies is one option, but you should pick whoever treats you well.
- The DME handles the Medicare paperwork. A good supplier will check your Part B status, collect the chart notes, and submit the claim. If your paperwork is clean, you usually get your first shipment in 7–14 days.
- If you’re denied, don’t panic. Most denials are paperwork issues, not eligibility issues. Here’s the exact process: How to Appeal a Medicare CGM Denial.
The Real Takeaway
A CGM is not as scary as it sounds. Millions of Medicare seniors are wearing one right now, and the vast majority of them describe the same arc: hesitant, then curious, then wouldn’t go back.
You don’t have to love technology to use one. You don’t need to be a whiz with your phone. You just need a doctor who’ll write the prescription, a supplier who’ll handle the paperwork, and a little patience for the first week while you get used to checking your arm instead of your finger.
If you want the next level of detail — which CGM fits which situation, what Medicare actually pays, what to do if you hit a wall — start with The Senior’s Complete Guide to Diabetes Technology in 2026. It’s the hub I point everyone to.
And if you ever get stuck on paperwork, send me a note. I’ve been doing this for a long time. It’s what I do.
— Susie
A note on sources: Coverage rules referenced above are based on Medicare Part B policy as of 2026 and my direct experience processing CGM claims at Peak Medical Supplies. Device specifications come from the manufacturers (Abbott and Dexcom). Accuracy figures (MARD) reflect values reported in each device’s FDA clearance documentation. This article is educational and does not replace the judgment of your physician.
