There are videos on Youtube showing how to remove a transmitter without breaking the sensor. Here’s two; the second is shorter but the first is better focused. The only tools you need are two used test strips.
When the transmitter is nearly done for, a sensor change will elicit a warning “this is the last session with this transmitter, make sure you have another on hand”. I think that it then will not allow you to start another new session with the same transmitter, EVEN IF that sensor fails early.
That’s how it’s supposed to work. It appears to be purely based on time since activating the transmitter, not on measurement of the battery condition. Sometimes the transmitter battery dies early. In this case you get a “transmitter battery critically low” alert. When this happened to me a few months ago, it only lasted a couple more hours.
If this happens, Dexcom will replace the sensor, since you cannot [are not supposed to be able to] put in a new transmitter with the same sensor.
However, the transmitter is guaranteed for only 90 days despite normally lasting for 110 days. A few months ago, my transmitter failed at 91 days. Dexcom replaced the sensor but not the transmitter. (I already had a new transmitter and sensors on hand, so it was an annoyance but no gap in coverage.)
Just a few days ago, my transmitter failed (“battery critically low”) at 58 days during a sensor swap. I explained that I didn’t lose a sensor, but they are shipping replacements for both sensor and transmitter anyway. I guess they just assume that “battery critically low” means a lost sensor.
Just recently – past couple of months I think – I no longer have to wait on the phone to report early sensor or transmitter failure. The last two cases, I just filled out the support form online. With the simple sensor failure, I also had to respond to an email with a couple of other questions – just the basic questions they ask on the phone. With the transmitter failure, I did not even have to do that.
I’m not sure how the above needs to be adjusted if you have restarted a sensor. I gave up on restarting because I seldom get good results after a restart. For me, sensors fail at 8 or 9 days about as often as they go a full ten days. I have built up a few to experiment with as a result …