Changing Dexcom sensor without a restart: an experiment

We have been wanting for a long time to see what happens when you swap a sensor without stopping/starting it—tonight gave us the perfect opportunity. Today’s sensor was 4 days old and had been flaking all day, starting in the middle of a huge (369) hormonal peak this morning. It was off (hourglass or three question marks) for more than five hours today. We finally decided to swap it out around 11:40pm tonight.

My son removed the old sensor from his skin, installed his new sensor, and snapped his transmitter into the new sensor. Within a few seconds we got a point, then another five minutes later. The signal looked good: we were surprised. We let the sensor run for 30 minutes and calibrated it: it was only 4 off: I was flabbergasted! We had not calibrated for 12 hours, so even without a sensor change it would have been quite good :slight_smile:

Here is the curve:

We are going to keep on checking manual fingersticks and see if the sensor remains in phase with reality. But so far we are all surprised by what happened.


Based on my experience with xDrip+ this would be expected behavior.

When I do a sensor change xDrip+ on the phone requires it to be in place for two hours before it will show a reading. But I get uninterrupted readings on my watch, which is the device connected to the transmitter.

So it seems like the transmitter keeps broadcasting but the software on the phone just refuses to take the reading if the “stop sensor” command has been issued.

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Cool! G4 or G5?

Thanks for posting. I have been doing this with almost every sensor change. Sometimes if current sensor goes to ???, my G4 receiver won’t read new sensor right away. If it doesn’t read within 15 minutes, I do a stop, start sensor, and have to wait 2 hours. However, sooner or later the receiver gets to the point where it requires the 2 hour wait. But I can choose the time that works best.

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I’ve done this, but have had mixed results with whether it remains accurate. If the next reading is off by a lot, I just do a double enter and reset it all though.

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That’s what we were thinking too! Do you find that the new sensor location significantly affects the signal level?

It is not surprising. There is no unique identifier on the sensor, so the transmitter or receiver would not even know you did it.


I use arms and inner thighs. Location is only issue based on sleeping position when there is compression on the sensor.

Back to back calibrations, and more frequent just after sensor change get it back on track. And when possible, I change sensor when levels are flat.

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Just so I’m clear what you did and didn’t do…you did, or did not “stop session” before swapping them out?

We did not. So we are still running in the old session, but now we can pick when to restart. To us it is a big difference. I’ll update the thread with signal quality info soon.


Update after about 15 hours: the CGM is tracking well, signal noise is low, every fingerstick is within 10. We are preparing to restart the session, since now is a good time.

All in all, I give it a thumbs up. On the other hand, as @cardamom pointed out, it may not always work as well if the new sensor and the old sensor have widely differing signal conditions. But, in that case, resetting the calibration by doing a double-enter is easy enough.

From here on, when we lose a sensor and restarting a session is inconvenient right then, we will just swap the transmitter without restarting the session, then restart it at a more convenient time.


Unless your name is Beacher. :cry:


@ Michel I’ve done this for the last 4 sensor changes and had excellent, stable results each time (similar to your experience). I’m inclined to do this every time now as I don’t see any downside risk.

Any significant reasons not to do this?

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One potential issue. The reason Dex makes you wait 2 hours during a sensor start-up is to allow sufficient time for the interstitial fluid to build around the sensor and for the sensor to be able to read it. In their testing, reading immediately was not accurate enough. (just like the some of the other systems make you wait 12 hours I think?).

Anyway, if you don’t wait the first 2 hours, just be aware that the readings you get for the first few hours might not be as accurate. And you should definitely calibrate it after a few hours just like when you are using a new one on a proper restart.


The reason I don’t usually do it is that I will eventually be forced to do the 2 hours anyway because I use the Dexcom app, so might as well line that up with the new sensor, unless I absolutely have to replace a sensor due to failure of some sort before it’s due to be replaced (which is rare for me). if I used xDrip, which I think doesn’t force you to do that, I would probably do hot switches regularly and then keep tabs in the first few hours and either continue on if it works or do the double entry to reset it if not, and either way skip the 2 hour wait.



To address variability during the warm up period, when a sensor change out is planned, I’ll put the new sensor in place 2 hrs before the hot swap. @TiaG mentioned in another post.


I also calibrated ours right as we put it in, not several hours later. This way, it adjusts the baseline for the new one.

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Six days ago I restarted my G6 with xDrip+ by going to Stop Sensor then taping on Don’t Stop, Just Reset All Calibrations. Was surprised that xDrip+ restarted the G6 sensor, and my Dexcom receiver accepted the restart. Readings just continued on both devices. xDrip+ now shows Sensor Start: 1/3/19 (16d 22h). Dexcom receiver shows Insertion Time: 01/18/2019 and expiration 1/28. So far the sensor has still been accurate, with two flaky data points in the last 24 hours where the data was about 20 points lower than the smooth line.

I am using the Sony 3 watch as my collector, and xDrip+ January 10 version.