Apple Watch OS4 and Dexcom

So for all of the Dexcom/Apple Watch users out there, we actually got an interesting nugget of information from yesterday’s WWDC. Yes, in watchOS 4 the Dexcom sensor will be able to communicate DIRECTLY with the Apple Watch without needing the iPhone as a pass through!!! Awesome, awesome news and bravo to Dexcom and Apple!!!

When I heard this I wasn’t sure if I heard it right, so I took a chance and messaged Kevin Lynch from Apple on LinkedIn and he responded!!! Here was his direct response-

"Hi Mike,

Thank you! Yes the support for Core Bluetooth in watchOS 4 will enable direct communication between the Dexcom sensor and your Watch, without requiring your iPhone to be nearby. We are very excited to be enabling this!



For me, this is fantastic news. I can now leave my iPhone behind and still get my numbers on my watch. Whether it be for a jog, in the pool, coaching baseball, out to dinner with my wife, in a meeting etc. etc.


Wow, this would be awesome! Do you know if there’s any way to configure it so that you could get customizable warnings on the watch at varying thresholds based on trending arrows? I know Dexcom just gives alerts based on fall rate and the absolute low threshold.

I don’t have one now, so I don’t know much about them.

I hope there will be a way of keeping the display turned on all the time rather than requiring a button push to see the number. I wonder if high/low alarms will also be available. Those things would be great features.

Having the display on constantly might kill the battery though, if it’s not optimized for that.

Are the alarms currently available on the watch different from the ones on the regular Dex iphone app? Because you can customize both absolute and rise/falling rates on there. You’d hope they’d include that on the watch app too…

I don’t have a watch yet myself—I think I’m going to wait until the next hardware update likely due this fall, admittedly in part because I’m still not crazy about the design of the watch (doesn’t really fit my style well at all) and want to see if they make any tweaks I prefer and also what new features might come out before investing. Sounds like it will be well worth it though. Also could be a nice option for kids whose parents might not want to get them a phone.

We have an Apple Watch, yes, you can add Dexcom to many of the screen faces. When my son looks at the watch his Dexcom number is big and in the middle of the screen. Everything else is smaller and to the sides.

Mike, this is great news. Is this backward compatible with existing Apple Watches? I am always fearful that the improvements will only work when you buy new hardware.

@Chris I would assume so but not 100% sure. I would think any watch running watchOS 4 would have the capability.

@Eric - display automatically comes on with raise of wrist.

I have Dex complication on pretty much every face I use and it’s great. Any watch face that allows complications allows the Dexcom number and arrows.

Could you set the Apple Watch to vibrate if, say, the Dexcom number was less than 125 and dropping by 15, or less than 95 and dropping by 8, that kind of thing?

Not that specific. Hope to have that functionality in future updates.


I am honestly not sure what you will be able to set on the watch for alarms. In our use case the alarms are delivered by the phone, and we haven’t looked any further than that since you have always needed the phone and the watch to make the system work.

Hopefully, it will be individually configurable.


wow, that would be huge for daycare. Right now they have to check his receiver, which takes active effort and means they sometimes miss readings. We do have alarms once he’s low, but we prefer they treat the low before it becomes low. If they had a watch that just vibrated whenever he hit a threshold that predicted he would be low in 15 minutes, it would be so much simpler for them.

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From the Dexcom G5x mobile CGM User Guide:

“While the system works with different smart devices, they’re not interchangeable during a sensor session, so before starting one, select which smart device you want to use and stick with it throughout your session. You can’t use multiple smart devices at the same time, but you can combine the receiver with a smart device during a session.”

Sounds like a Smartphone and a [direct] Smartwatch is a no-go?

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I’ve been giving this some thought. Initially, I was really excited about the potential for my watch to be my display device. I’m with you, @mikep, I really would love to ditch my phone for some things. But as I’ve considered it, I can think of several things that make this difficult.

Let me say first that I LOVE my apple watch. I switched to an iphone for the first time after my diagnosis. I don’t love it, but I do love having my dexcom data available, though had I known about xdrip+ at the time I might have tried that before making the leap.

-The apple watch has to be charged. It says it requires charging every 18 hours or so, but I’m not sure that projection includes the number of times I glance at my watch daily to check my bg. Draining the battery with every glance, albeit, not by much. This means that each time the watch would need to be charged (requiring about an hour every 18 hours or so), the watch wearer would not have access to live readings (unless we had the capacity to follow with our phones. Will we?) This would be like having a mini restart-session every 18 hours.

In the short span I’ve used an Apple watch, I’ve become addicted to wrist readings so much so that I hated being without it for the charge period. Since one had been gifted to me, I went out and bought a second one, so that I could alternate and never have to lose wrist readings. Over the top, I know. But it’s been working.

With this new option, it sounds like we won’t be able to toggle between devices, right?

One other difficulty I see with this is the display screen. The watch screen yields a limited view. The most it will display is 6 hours at a time, but with my phone I could easily take a look at the last 24 hours and scroll through individual readings. Any workarounds there?

-is this update currently available?
-also wondering how one enters data on the watch after a session startup. Presumably, it’s not too difficult?

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Perhaps you could continue having the Dexcom transmitter go to the iPhone. And then the iPhone transmit to the Watch. The Dexcom would not know about the watch so I guess that would be an Apple question?
As to charging, do you have one of those portable batteries about the size of a lipstick? Those are great.

When I is watch OS 4 due out? When will this function be available?

watchOS 4 is out. Is this functional yet?

Word here is that it’s not yet functional for direct to cgm. It should be, but apparently there are some kinks to work out. Dexcom direct to Apple Watch It appears that Fitbit may beat them in the race to cgm watch

Seems as if the Fitbit integration is no different than the AW at this time.

Initially, Fitbit Ionic will likely display data relayed from the Dexcom G5 phone app, just as Apple Watch and Android Wear currently do (“secondary display”). Over time, it’s possible that direct CGM-to-watch communication might be added – this would allow CGM data to be sent to the watch without the phone being present (“primary display”). Dexcom is already working on this direct communication with the Apple Watch, though there is no timeline on when it might be available. We see big convenience potential in such an update and hope it comes to Fitbit too.

This one is on Dexcom. They need to enable the transmitter to watch conversation ASAP. Apple has done their part with enabling Core Bluetooth in watchOS4. Not sure if there is a regulatory issue at play or not. I would assume not as the watch is simply displaying the data, no different than seeing on the iPhone.

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Might be a bold assumption since they couldn’t even figure out how to link it to android phones (unless the user somehow hacks them) and like half of the target audience uses them… I think that was some sort of goofy regulatory nonsense. Regulations are great!

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I find it odd that Dexcom was part of the Apple WWDC way back in June and the OS has been released for over a month and this functionality is still not available. Why were they part of the WWDC if the new OS did not bring this functionality?