G5 data with no 2-hour warmup for new sensor (using Dex app on phone and Dex receiver)

I use the Dexcom G5 with the Dexcom app on a phone. I also use the Dexcom (new-style) receiver for “microwave technique” restarts so that I continue to get CGM data during the 2-hour restart warm-up. But when I actually change to a new sensor, until yesterday I hadn’t figured out how to continue getting CGM data during the first 2 hours, even though I think that some people on this site already know how to do it and all the pieces have been described here in various threads.

So I’m going to say simply how I do it. (I acknowledge that for folks using xDrip+ or Spike, they may not have the issue of no data during the 2-hour initial warmup.)

The first ingredient is the “microwave technique” for restarting a currently running G5 sensor when using the Dexcom phone app for primary CGM and a Dexcom receiver is available. It must be done more than 2 hours before the current sensor session expires. I actually do it on day 6 and 12 so that there’s no danger of running out of time. So here’s my version of "The Microwave Technique,"using the Dexcom app on a phone as my primary CGM, and the Dexcom receiver to help restart.

  1. Bring the Dexcom receiver within range of the transmitter and wait for it to connect to the CGM session that’s currently running on the phone. That generally takes 5 to 15 minutes.
  2. Wait for a fresh new CGM reading to arrive on the receiver.
  3. Wait 1 more minute, then within 2 minutes do the next 3 steps (must be before the next transmitter communication.)
  4. On the Dex receiver, Stop Session.
  5. On the Dex receiver, Start Session.
  6. Put the Dex receiver in a radio-proof container. I use a metal cookie tin. Some folks use an unused microwave oven. Some have a proper Faraday bag. Some folks just move the receiver way far away out of radio range.
  7. Wait at least 2 hours 15 minutes. (I don’t know if much much longer will cause problems, but a delay of 3 or 4 hours seems to be ok.)
  8. Remove the Dex receiver from the radio-proof container, wait for it to reconnect to the transmitter (typically 5 to 15 minutes), and then wait 5 minutes or less to get the “Enter first calibration” request on both phone and receiver.
  9. Enter the first and second calibrations on the phone, and put the Dex receiver away.

But what about when a new sensor is inserted? Other folks on this site have already told us that during a running sensor session you can pop the transmitter out of the old sensor and snap it into a newly-inserted sensor and it will continue to give readings with no warm-up time, but when I tried that I wasn’t getting good CGM data. Some folks live with it and just keep recalibrating until it seems to work ok, but I wasn’t happy with that, so I’ve been waiting 2 hours without data when I start a new sensor.

Yesterday I finally figured out how to fix that (after smacking my palm on my head to acknowledge being a slow learner). Simply stated, after switching the in-session transmitter to a new sensor, just do the microwave technique to start a new session without losing data. The detail is as follows.

When the sensor is still giving data but it is old and jittery so that I want to change to a new one—and more than 2 hours before the current sensor session will end (well before so there’s no danger of having the running session expire) do this.

  1. Insert a new sensor.
  2. Without doing a Stop Session, pop the transmitter out of the old sensor and insert it into the new sensor. The Dex app should continue to receive CGM data, perhaps missing one 5-minute interval.
  3. Calibrate if the CGM is reading wrong.
  4. Use all 9 steps of the microwave technique listed above to start a new sensor session while continuing to receive CGM data in the phone app. After 2+ hours, you’ll have a fresh new sensor session on a fresh new sensor, without having to go 2 hours without CGM data.

Or you could just use xDrip+, if that’s your preference.


So you’re saying same exact process as before with the added step of taking off the old sensor, inserting new sensor (with old transmitter) after your put your receiver into the microwave (after stopping/starting session on the receiver)?

Haven’t tried it, but certainly will. Never even thought about trying this before. Will give it a go next change out.

I’m just surprised that changing out the sensors/transmitters doesn’t cause problems with the G5 Mobile app (that has the current numbers running). But you’re saying only a few bleeps disappear and it reconnects as soon as the new sensor has been inserted (after a few minutes).

Thanks for this info!

I did it a little bit different order from what you write. First I put in a new sensor and move the transmitter over to it while the CGM session is running (on the Dexcom phone app), and after I see a CGM reading from the new sensor (happens soon, like within 5 or 10 minutes), then I do all the steps 1–9 of the microwave technique to start a new session without losing data. I’ll edit the original post to try to make that more clear. I haven’t tried what you say, putting the receiver into the microwave before moving the transmitter onto the new sensor. Maybe that way works too.

Other folks have posted on this site that it works, so I tried it.

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I suppose we did something wrong because we followed these steps and ended up getting question marks after switching them out…and it’s been over 30 min now. I just stopped and restarted receiver and put it in the microwave and will wait the 2 hours and check him every 30 min between. Below is what we did and it’s possible I still didn’t understand fully so if that’s the case, feel free to correct me (again.)

Simply, we installed the new sensor on his other arm. After that, Erin pried open the old sensor and I pulled out the transmitter. Cleaned it and waited for it to dry, then inserted it into the NEW sensor. Immediately after that we DID get a single number appear, but then five minutes later, the numbers disappeared and we got question marks. We waited a full 30 minutes in the hopes that the numbers came back, but once they didn’t look like they were, we just stopped/restarted sensor and put it in the microwave and are beginning our 2 hour wait period.

If we still did something wrong, plz let me know.


Wow, I just started getting the numbers! It’s been an hour since we did the changeout and the receiver is already in the microwave, but I just got a message on the iPhone for calibration needed…entered BG’s twice and now I see numbers. Not sure what happened, but I guess it’s good that we’re seeing numbers after only 1 hour instead of the full 2. Will see what happens up to and after the point of removing the receiver from the microwave.

Even more strangely, after the receiver was in the microwave for 2 hours, we took it out and waited for it to get signal, but after it gained signal it suddenly went to the clock screen showing 30 minutes remaining…then the phone turned into numbers it did have, into the clock as well. Now (even though 2 hours was done), we still according to the receiver/phone, still have time to wait. lol.

That’s quite a wild series of events. I can make up a plausible story to “explain” what happened, but really I’m just guessing. One slight difference in technique is that I cleaned, wiped, and moved the transmitter across sensors in a very short period of time, whereas after you cleaned it you waited some time for it to dry, which may have spanned across a 5-minute transmitter time boundary with no signal. So maybe that’s one difference.

Anyway, suppose after you switched the transmitter to the new sensor, it turns out that the new sensor was giving a significantly stronger raw data reading, so because of the sudden drastic change the app showed ???. Then after the app saw a consistent signal over the next half hour it met the criteria for usable data, but because of the large change it wanted a calibration to be safe.

As far as getting a half-hour time to go when the receiver came out of the microwave and reacquired the transmitter signal, I’m guessing that the receiver just needed more time in the microwave, because my routine experience is that it only takes about 5 minutes before asking for the double calibration.

Maybe this is it. I did try to do the entire process before the 5 minutes was up, but it’s very possible that I missed it and that’s what caused this. We didn’t even look at the time so you’re probably right. Next time we’ll a) install sensor, very importantly b) WAIT for a new number to appear on the old sensor/transmitter, then c) IMMEDIATELY remove transmitter, clean quickly, then install immediately.

Erin also reminded me that AFTER we installed the new sensor but BEFORE we stopped the old session, we received a calibration blood drop and we did a calibration between there too. We got a number appear from the new transmitter AFTER we we calibrated and THEN we stopped/restarted the receiver and put it in the microwave. So a combination of all these things probably caused what we saw. Is it normal that you receive that calibration blood drop after removing the transmitter and putting it on the new sensor or was that just cooincidence?

That sounds like the way I did it.

I haven’t experienced that, but it makes sense to me that it could happen if the new sensor is performing significantly differently than the old one.

Anyway, after we all get more experience with this maybe we’ll be able to figure out the best way. In any case it seems better than what the G6 users are going through: they seem to have to take the 2-hour warmup without data even when restarting the previous sensor, not just when starting a new sensor.

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