For those of you that are able to get past the 7 days with a single sensor, what clues do you have to tell when the sensor is beginning to no longer provide accurate readings. I have done a restart of my second sensor to see if I can continue past the approved 7 days, and I am not sure of what I should keep an eye out for. So far, I have been very pleased with the readings I am getting from the Dex - even during the night (which was a big problem when I used Medtronics). Thanks for any hints you can share!
Thank you, Korrie, for your input on this. I have found the seond 7 days to be far more accurate, and consequently comfortable, with regard to the dex sensor…especially at night, as you point out!
I am sorru. that was a bit of an incomplete entry on my part…didnt really respond to your comment at all! I find that around day 11 or 12 it starts to REALLY itch…then I start getting unprovoked ???"s and that tells me it is time to change it. good luck, and PEACE
I’m only on my second sensor so i’m a newbie BUT i did reset my last sensor and made it to day 11. I had great readings but all of a sudden starting getting ???. It was itching enough that I was excited about an excuse to remove it so I did!
I had bled a little with insertion and it turned out I was completely bruised under the sensor pad-maybe that’s why it didn’t last long. Not sure.
Good luck!
When my sensors go bad from age, I usually get trends that tend to steadily creep up OR down (often by a large degree… reading LOW when I am in the 90’s, or trending up over 200 for the same)… and they use a large degree of variability that a fresh sensor often displays (quick rises/declines) which doesn’t match what my fingersticks say.
In my experience, ??? on an older sensor is usually due to moisture getting to the sensor wire - either from sweat, or showering/swimming. You can usually seen condensation on the inside of the sensor housing (most easily visible through the side away from the clips) Sometimes it will recover if it is able to dry out, but usually it will happen again just as soon as it is wet in any way again.
Edit - sorry, didn’t mean to reply specifically to Sarah.
I’m new at this as well. My first 3 sensors lasted 14 days (intentionally replaced), 16 days (sensor fell out), and 13.5 days (sensor fell out). In both cases the sensors fell out while exercising. I ordered some flexifix today based on recommendations here.
I think that a big part of the sensor lifetime that isn’t discussed much is the actual enzyme material that the sensor is coated with. It only lasts so long and my suspicion is that the enzyme gets “used” up faster when your blood sugar levels are higher. This could partially explain why some people don’t seem to get as much life out of theirs.
I very much second what Sarah said, it’s the very steep rise or falls of the BG readings that give the first hints of an aging sensor. You’ll find that the BG values during times of flat BG are quite OK, but it’s rodeo time around the meals.
Do yourself a favour and don’t try to “follow” the Dexcom using insulin when you see a steep upward trend, that will bite you back. Believe me, I’ve done that! 
Ciao, Luca