That makes sense. Maybe when each transmitter is removed from its magnetic shoe it will start the countdown. If true, that means the second transmitter will not start its 90 days unitl the first 90 days expires. The customer service rep at Dexcom did not have a ready answer for my detailed questions. I’m sure the facts will become clearer in the months ahead.
It appears that Dexcom is updating their web page as they get more experience with customer questions/concerns.
Here’s the latest on G5 transmitters copied from their FAQs:
How long does the Dexcom G5 Mobile transmitter last?
Your Dexcom G5 Mobile transmitter is covered under a limited warranty for three months, starting from the shipment date. Once you see the transmitter “Low Battery” screen, replace the transmitter as soon as possible. Your transmitter battery may drain as quickly as one week after this alert appears.
One explanation that I hadn’t considered is that the warranty may start as a function of the shipment date while the 90-day hard limit for service may be triggered when the transmitter is removed from the box.
I wish therir written communication was more precise on day 1 but at least they are using their experience to further clarify things.
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For those with the Share receiver I’m sure you have noticed that if your iPhone is out of range of the Dexcom receiver for a period of time that once they communicate again all the ‘missing values’ get filled in automatically. However, this is not true if the Receiver is out of range for an extended period of time.
With the G5 does this mean that it will be almost impossible to miss readings?? Since the transmitter will now store the values will it ‘backfill’ when it connects again the iPhone? This is a great PLUS on my list.
Just got off the phone with Dexcom and clarified a couple things that may be of interest. It turns out I’m eligible for a free upgrade because I have a G4 Platinum Share, purchased in April. It’s basically going to be a matter of doing the scheduled transmitter replacement at the 6-month mark (which for me is October), except they’ll send me a G5 transmitter instead of a G4, along with an authorization code that will let me upgrade my receiver. Apparently with a Share they don’t have to replace the receiver; it just requires a firmware upgrade, which the auth code will let me do over the Web. [edited to add:] after the firmware upgrade the receiver will no longer receive from G4 transmitters, so it is a one-way change.
Adding: the tech guy I talked to also confirmed that it’s the Bluetooth battery usage that is responsible for the shorter lifespan.
I often wonder if a rechargeable design would be cheaper but I don’t get the impression that the Medtronic system is any cheaper than Dexcom. It would really interesting to be a fly on the wall when Dexcom discusses these decisions. 
Do any of you have an idea how much it will suck the IPhone battery? I don’t have much experience with Bluetooth technology… I have an old the 4S and I’m worried about how fast it will drain.
I’m using the Dexcom G4 share system now with my iPhone 6. My iPhone is connected via bluetooth from the receiver, not the transmitter. I don’t notice any appreciable drain on my iPhone battery now. I don’t see how the G5 would be much different in its duty cycle than the current G4 share system. Just a guess on my part.
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Has anyone heard whether Dexcom will continue to sell G4 transmitters? I’d rather have a smaller transmitter than one that transmits to a phone…
As an adult not using Share, I don’t see much benefit to having data on my phone. The G4 receiver fits in my pocket, but my phone does not.
The only reason I’d want the G5 is if they were to allow direct communication between a watch and the transmitter (without requiring a phone in Bluetooth range). I’d buy any watch solely for this purpose.
I have the same question. My daughter just uses the G4 with the plain receiver, no share or anything like that. We don’t want smart phones or any other stuff. I hope we’ll still be able to keep the same system.
The G4 will have to remain available for the foreseeable future because the Vibe and other pumps that will be incorporating the Dexcom (OmniPod, I think) use the G4.
I run Share on my iPhone 5 and I don’t see any difference. My favorite use-case is bike riding with the app running on my phone in a holder on my handlebars. I turn the “sleep” preferences off so it stays on the whole time and I can monitor my BG for the sudden, sharp lows I’m prone to when exercising. Very handy! And it doesn’t run the battery down noticeably. I usually have an Audible book running too.
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Please note that the Libre is no CGM. There is no permanent connection between sensor and receiver. You have to “scan” the sensor (move the receiver over the sensor manually) to get the actual glucose level and the data since last scan.
There are no alarms! As this is one of the most important things with my Dexcom the Libre would be not alternative for me.
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You’re right, Johann. I’m aware that the Libre is not a direct replacement for a CGM. It’s really a better replacement for fingersticks.
I don’t own and have never used any Dexcom product. But I doubt it.
The reason the missing values are “backfilled” to the iPhone once it comes back into range of your G4 Share receiver is most likely because the Share receiver has stored those values. My understanding is that neither the G4 nor the G5 transmitters buffer (save) any values if they are unable to transmit them to a receiver.
Another question here is whether this “backfill” will actually disappear when switching to the G5. I believe the G4 always talks directly to the (share) receiver and the share receiver then can, optionally, also forward the data on to an iPhone/iPad or Apple watch. I think the G5 might actually have separate Bluetooth connections to an iDevice and its receiver. So if the iPhone is left behind and goes out of range of the transmitter then any missed values may remain missed even if the receiver was able to catch them.
Or versa vice, of course.
But that’s just a guess, of course.
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That’s my understanding of things, too, @irrational_John. I don’t believe the Dexcom G5 transmitter actually stores any data, so if you go out of range, you’ll lose data just like with the G4.
Incidentally, I just heard a podcast the other day where one of the executives at Dexcom implied that the G5 transmitters would not automatically expire at the end of three months, and would be usable until the actual battery died. He said that the cost of the G4 and G5 would be comparable for users. I guess we’ll have to wait until people are able to use it and report back, since there is confusion around this issue.
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Oh - that’s why I don’t see the option to upgrade on their site - only those w the authorization code will be able to - interesting. Thanks for that info.
No, the option to upgrade is there, though you have to create a login and they have to have you in their system as the purchaser of your existing one:
http://www.dexcom.com/faq/what-upgrade-offers-are-available-dexcom-g5-mobile-cgm-system
I started to do it online but ran into a snag because my order was placed through Joslin clinic’s diabetic supply coordinator, so Dexcom doesn’t have me on file. I had to go back to the coordinator to do it.
The authorization code is a separate thing–they give you that as part of the upgrade, if you have a Share-capable receiver, so you can update the receiver’s firmware to communicate with the G5 transmitter.
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Thanks! Yes - that’s actually what I meant by “upgrade.” I realize that’s not the best term considering the situation. I should have said “update.” 
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Gotcha–that’s correct. I got into a little more detail with the tech sales rep, who confirmed that you’ll get a link to a special page for this along with the code. So it’ll be: connect your receiver to your computer’s USB port, go to the link they’ll provide, enter the code, get the update.
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