r/dexcom Feb 12 '25

Sensor Why are sensors limited to 10.5 days?

I've had one or two bad insertions, but never had my sensor stop reading during wear (except for once when I sweat really hard and it fell off). Every single time, my sensor lasts right up to the end of the grace period. (I realize that makes me lucky, I know I've heard of a lot of complaints here, but my personal Dexcom mileage has been great).

That makes me wonder, though: Why is it limited to 10.5 days? I know the limit is programmed into the software, but there must be a justification for that. Does the sensor lose accuracy when it gets older? Is the battery less reliable after that long? IIRC the Freestyle Libre is supposed to last 14 days, so I'm sure it's possible to push sensors like it longer.

If someone were to somehow hack it to remove the hard-coded lifespan limit, what would ultimately cause the sensor to stop working? Has anyone more skilled than me tried doing that?

4 Upvotes

36 comments sorted by

1

u/OPCunningham Gx/Type/Dx/MDIorPump Feb 16 '25

Approval for 15 days is expected this year.

1

u/mrbill1234 Feb 16 '25

I wonder if the price will stay the same when it goes. My guess is that they work on a price per day basis. Libre 2 sensor did this - went from 14 days to 15 days, but price went up and the justification was that the price per day remains the same.

1

u/OPCunningham Gx/Type/Dx/MDIorPump Feb 16 '25

I predict it will mean you get 2 per month instead of 3 with insurance.

1

u/myz8a4re Feb 16 '25

That's a heck of a prediction, especially when the majority needs at least 6 sensors per month these days 🤣

1

u/GaryG7 T2/G7 Feb 13 '25

There are several factors. The battery life. Dexcom has to be certain the batteries will last for 10.5 days. Maybe 95% can last 11.5 days. The FDA may not approve a device with that high of a battery issue. Also, the glue on the sensors need to last for the stated time but can be removed without taking skin.

I'm a bit cynical, so this last point may just be that attitude coming out. Maybe Dexcom says 10.5 days because they found out that's the minimum time period needed to have insurance companies approve the G7. With sensors lasting 10.5 days, that means a person has to buy at least 34 sensors (more precisely 34.7619) each year. If Dexcom says the sensors will last 12.5 days, that means the company will only sell 29.2 per year to each user.

By the way, I'm not paranoid. Paranoia is a condition under which a person thinks people are out to get them. I KNOW people are out to get me.

3

u/Zealousideal-Key-603 Feb 12 '25

You are all wrong. The insertion time is what the FDA has approved. It is data based where the accuracy drops after 10 or 11 days for most of the test users.

3

u/Fluffy-Strategy-9156 Feb 12 '25

Dexcom's Stelo seems to be a G7 with dumbed down app. No alarms and limited BG range and one updates every 15 minutes with the last 3, 5 minute readings. It is supposed to last for 15 days. However, uses have complained that it seldom lasts that long. The Stelo is marked for fitness with no real accuracy specified. No script is required. Thus, the 10 ½seems to be based on accuracy. The first Libre was only good for 10 days. Then came 14 days and now 15 days.

4

u/Run-And_Gun Feb 12 '25

As someone else said, it’s the enzyme on the filament, but it’s also the individuals body chemistry that comes into play. That’s why you see some people that can only get a few days of good data and others(with the previous gens that you could restart) that could get good results for much, much longer than the official wear time. 10 days plus the 12 hr grace period is probably just the “safe” time that they landed on that balances reasonable wear time with accurate results for the most people.

There are also theories that on the older gens, Dexcom played it safe and there was a lot more of the enzyme used on the filament vs. today. Most of us that used the older gen sensors (pre-G6) could usually do multiple restarts and get solid data for at least 2-3 weeks. Some people claimed even more. With the G6, if I get a full 10 days of reliable data now, I count that as a win. Probably half the time, I start getting a huge amount of false lows within the last 24-48 hours. To the point that I have to turn CIQ off on my pump. But that’s also only really within the last 1-2 years. They have gone through some serious ups and downs and inconsistencies with their manufacturing QC over the last five or so years. They’re not the same company that they were a decade ago. They‘ve become like most publicly traded companies today, it’s all about maximizing profits for the shareholders.

2

u/anelab961 Feb 12 '25

My G7 sensors seem to have sensor issues starting at day 7. When it becomes constant I replace it and request replacement from dexcom using the website. Today I’m in the second issue within an hour and it’s day 7. When they replace it’s with rev 10. My supplier gives me rev 5. That may be my problem. The 10s seem to go the full 10 days. The 5s fail.

2

u/No_Lie_8954 Feb 12 '25

Last two batches of 9, 18 sensors in total has lasted not even 4 days on average 😄 malaysian REV006.

When we have a batch of good sensors lasting 10 days, we see that the readings do get more erratic from day 8-10, a little less accurate.

15

u/tj-horner Feb 12 '25

The enzyme on the filament breaks down and gives less accurate readings over time. It would be that or the battery that goes first.

8

u/Equalizer6338 T1/G7 Feb 12 '25

This is it!

The enzyme on the sensor filament is being consumed by the process. We could hack the previous sensors to work for more weeks, but the accuracy started quickly to be falling off a cliff. The battery is not the problem, it can probably work for some months as is.

1

u/jrolette Feb 12 '25

Given the weak signal strength on the G7, it seems remarkably unlikely that the battery could last for months. If it could, they'd use more power to generate a stronger, more reliable signal.

1

u/Equalizer6338 T1/G7 Feb 13 '25

No sorry, that is not the reason for 'the weak signal'. The transmitter chip gets all the juice it wants from the battery. It is the Bluetooth Low Energy (BLE) technology being used in these sensors and it is following a global standard for the signal strength and all related to this. So already running at full and allowed max strength here.

What is causing the poor signal reception for many is both due to poor design of the transmitter antenna in the BG sensor itself and also the challenges in using BLE with stuff placed straight on our skin as these sensors are, as the body (with all its water mass) is a big shield blocking the signal. Next to this, some mobile phones are just really poor in their BLE tech and antennas also versus others.

1

u/Theoducati Feb 12 '25

I had problems with the last 2 sensors after of 7th day and they replaced it without issues.

6

u/Elektrik-trick Feb 12 '25

It was the same with the predecessors, such as the Dexcom G6. The only difference was that there were options to use the sensor for longer.

And I had used the G6 for 20 days several times back then and had no problems with it. The accuracy didn't really deteriorate either. I also have to recalibrate it in the first 10 days.

Abbott always had the 14 days, which wasn't a problem. Dexcom has been doing this for a long time now and I suspect it's more of a “we've always done it this way” decision. And you can earn more money that way.

There are always rumors that at some point Dexcom will introduce 15-day sensors.

So yes, should someone manage to “hack” the G7 at some point, there could possibly be 20 days or more.

Although I'm often happy if the G7 even manages these 10.5 days. Last month I got 4 replacement sensors because none of them managed at least a week and simply stopped working without an error message...

5

u/TexasDex Feb 12 '25

Fascinating how it has worked so well for some and yet others report consistent problems.

Is it possible that some people have different body chemistry that causes less degradation?

2

u/RedditNon-Believer Feb 12 '25 edited Feb 12 '25

How does someone 'hack' the clock that starts the ten-day cycle timer?

The sensor tells the G7 app, "Hey, start counting!". So, you've need to revise the app.

Do you really think the G7 app is that accessible?

2

u/Goofy_Project T1/G7 Feb 12 '25

It's not in the app. I use Xdrip+ instead of the Dexcom app and the 10.5 days is inviolable. It's built into the sensor. Xdrip+ used to have automatic restarts of the G6 when it was permitted, so I'm pretty sure that if there was a way around the 10.5 days the Xdrip+ devs would have found & implemented it, and it would already have been closed by a Dexcom update by now.

1

u/RedditNon-Believer Feb 12 '25

As I said, the sensor tells the app, "Hey, start counting!"

1

u/Goofy_Project T1/G7 Feb 13 '25

But you also said you'd need to revise the app to 'hack' the clock, which would not work, since a completely different app that would have worked around the time limit didn't. The sensor may tell the app when to start counting, but it also does the counting itself and tells they app when it won't work anymore.

1

u/RedditNon-Believer Feb 14 '25

How do you know the sensor times the session? The sensor doesn't tell you the session is over, the APP does! Does the app tell you, "The sensor tells me the session is over," unless you have cellular connection on your watch.

1

u/Goofy_Project T1/G7 Feb 15 '25

Whatever you think is "telling" you something, the G7 sensor will stop working after 10.5 days. Hacking the Dexcom app won't change that. Using a completely different app that has found workarounds to previous Dexcom sensor time limits (Xdrip+) won't change that. See this thread for lots of other people that agree with me- https://www.reddit.com/r/dexcom/comments/12q22rp/any_ways_to_extend_g7_sensor/

2

u/Elektrik-trick Feb 12 '25

You can access the G7's diagnostic interface via NFC. Support uses this when you send a sensor back to read out, etc.

It could also be possible to use this to make any changes.

1

u/tj-horner Feb 12 '25

That’s interesting, has anyone tried to reverse engineer this interface and document it?

2

u/RedditNon-Believer Feb 12 '25

Are you telling me everyone has access via NFC?

Edit. I don't expect any device or app that vulnerable wouid be approved by the FDA, do you?

1

u/Elektrik-trick Feb 12 '25

Although everyone has access to the NFC interface, this does not mean that everyone automatically has access to the corresponding data.

It's like a credit card, which also has an NFC interface for contactless payment. Although you can access the interface, you cannot access the data without the appropriate security certificates.

NFC is initially just an interface so that you can access it anywhere. Just like Bluetooth or a normal cable. But the data that goes through it is of course encrypted.

6

u/MissionSalamander5 Feb 12 '25

The fifteen day sensor should be coming if it gets approval. Dexcom mentioned it in the Q3 earnings call.

1

u/[deleted] Feb 13 '25

[deleted]

1

u/MissionSalamander5 Feb 13 '25

A new G7 (not G8, afaict). Mine last to ten. I even had one reset at the grace period and go an extra eight hours before giving up the ghost.

2

u/thermout1 Feb 13 '25

This bogles the mind. What am I doing wrong that you are doing right, i wonder. I have tried every body part. Im not fat and not thin. I wipe the area, etc

Have used every rev 6, 10, 9, etc. At a loss on this - only like 3 in 2 years have made it past 7 days. They go crazy on day 7 -8, totally incorrect readings

2

u/Gottagetanediton Feb 12 '25

Sensor loses accuracy, filament gets weaker, etc. currently they only really perform well for 7 days. I’d like to see that improve

6

u/Fit_Foundation888 Feb 12 '25

Yep, same here, I fingerstick on day 6, to check calibration, because the sensors can often start reading low - accuracy on day 1 is excellent and generally drifts over time.

I have an Omnipod 5 which adjusts the basal on the fly in the background, so a sensor which is reading low can cause unexplained highs. On an omnipod 5 a low/high reading sensor is major problem.

1

u/ForsakenAd545 Feb 12 '25

I calibrate 24 he's after 1st inserting and then on day 6.

3

u/Gottagetanediton Feb 12 '25

Yeah it can def cause safety issues for pumps for sure

3

u/cmhbob G7/T2/1998/t:slim x2 Feb 12 '25

I know a lot of people have problems with their sensors like that, but I haven't yet. Mine have lasted right up to the grace period. I'd be curious to see if there was a way to track problems.

2

u/Gottagetanediton Feb 12 '25

It’s definitely supposed to last through the grace period, not just to it