I just thought I'd throw out some information for anyone who might be interested in using the G4 while surfing or swimming in the ocean. For me, surfing is really the number one place I'd prefer not to have a low. Even when surfing with friends, you are still mostly alone when you are in the water; well except for the sharks. The G4 has, so far, been kind of a mixed bag when it comes to surfing but here is what I've found. Hopefully it is helpful to someone else.
First, the receiver isn't waterproof. This is kind of a bummer since cheap waterproof electronics have been around forever.
Second, I've had success bringing the G4 receiver out into the water by sealing it up in an aloksak bag. The 3.37x6.37 bags made for cell phones work great and they've actually worked perfectly thus far.
Third, I tuck the receiver into my wetsuit on the outside of my thigh. This keeps it secure and out of the way.
Fourth, the transmitter is really not a bother even on my stomach. Your mileage may vary but I don't ever notice it.
Fifth, so far the actual operation of the G4 is a bit sporadic while I am in the water. I don't ever look at the receiver while I am in the ocean (it's buried in my wetsuit) but when I look at the readings afterward I find that there are large gaps in the data. I can at least discern that there are peaks and valleys but the general trend is downward so the G4 has been at least somewhat useful.
Sixth, I haven't had a low alarm in the water but judging how it makes me jump when it goes off in my pocket I am guessing I'd feel it even in the ocean.
Last, I probably won't wear the device all the time, just enough to help me predict what is likely to happen on future outings.
For windsurfing I found it too unreliable in the water. Numbers were all over the place, and it was a pain to keep track of it. It just worth the risk of loosing it when it's not even functioning well. I just come in every 30-60 minutes and make sure all is well before heading about again. Snorkeling is a little different, and I did carry my dexcom in a double layered roll top bag (water WILL come in these bags when they sit in water, hence using 2 layers). With light swimming, it still functioned very well. I'm not sure if surfing sports with constant in and out of water is what causes the problem (or the occasional laying on it?).
Hi Andy, thanks for your reply. It's really helpful to hear others dealing with similar issues and double-bagging is surely the way to go. It's helpful feedback that you are getting unreliable readings with windsurfing but OK results with snorkeling. I may just have to experiment a bit more with different positioning, etc.
I also share your concern about losing the device. I almost lost my receiver in the first paddle out. I had it strapped to my thigh with a spibelt and when I checked to make sure it was OK I found it dangling from my foot, milliseconds before it would have drifted into the great, wide ocean on it's way to some distant land.
It did, however, give me enough insight to decide that I am always going to take carbs after 20 minutes of surfing no matter what, just to be safe. No matter how many carbs I eat before I go, it's not enough to last me through a whole surf session.
I would highly recommend putting a cord on it if you can. The Aloksaks can't do that if I remember correctly, but there are other waterproof zippered pouches than can. Similarly, I occasionally use a GoPro camera, but the plastic mounts are plastic and could easily break off and the camera will quickly sink, so I use a thin cord to make sure it won't be lost.
I was also worried about the Dexcom sensor peeling off, especially now with the bulkier G4. I have lost pump sites before from surfing (guess it got rubbed quite a bit). For (wind)surfing I take the pump off to keep it safe, and I'm usually burning enough energy that there's no issue with that. I kept it on for snorkeling, with the pump in a zippered pocket. I probably wouldn't keep it attached if I was expecting to be in water too deep to dive in case I needed to retrieve it.
Great advice Andy. Thanks.