Slight clarification: the Apple Watch Ultra has a water resistance rating of 100m. The Oceanic+ app has a 130ft/40m limit because that's the recreational diving limit.
There is virtually zero risk of an oxygen toxicity seizure in the 1.2 - 1.4 atm range. I don't think there has ever been a confirmed case of a sport diver toxing at that level. We normally target about 1.2 atm for the working phase of the dive (reduce slightly for long exposures) and 1.6 for deco (with back gas breaks for long oxygen stops).
Narcosis is an issue with nitrogen and oxygen (as well as most other gasses). Helium is the exception. It is a noble gas and has no real narcotic effect; rather the opposite. Other noble gasses such as argon are much more narcotic than nitrogen and aren't used as diving breathing gasses (outside of a few limited experiments).
The other problem with nitrogen and oxygen is that they are relatively dense and so at greater depths they cause increased work of breathing, which in turn causes CO2 accumulation. CO2 is itself highly narcotic, and has other negative physiological effects. So for deeper dives we add progressively more helium to the mix.
Oh, cool! It looks like that's the limit of Apple's Depth app, as well, which is what I found when I searched, and assumed it was the limit of the watch.
Well that's definitely better - I wonder what happens when you go under 130 feet, though. A dedicated dive computer would at least provide accurate information, rather than throwing you to the wolves because you exceeded some legal limit.
Also on the plus side, some of the existing air pressure transmitters use bluetooth, so if they could get that working, they'd actually be one of the cheapest air-integrated computers on the market.
(edit: they do not use bluetooth, they use low-frequency radio ~38khz)
I think I'll stick with my Shearwater Peregrine though, pros and cons considered.
DC Rainmaker showed what happens to the watch when you take it past the max depth in his review [1] (using a pressure chamber).
I think your concerns are valid and merited for your very advanced level of diving, but at the same time the vast, vast, vast majority of divers aren't going anywhere near 130 feet. If I were going on a standard "simple" dive to <60 feet, I think I'd be pretty comfortable with just the apple watch ultra, a dumb watch + cheap depth guage and a written back-up plan.
Yes, agree completely. Would be happy to have just this on a 60 foot dive. And will be happy to see it on the wrists of other divers on the boat, as I think it will make them safer vs the status quo. Just wouldn't _buy_ it for that purpose myself, I think there are better options if you research a bit.
Also, I never dive past recreational limits, I'm not a technical diver by any means. I would simply have philosophical concerns about a piece of equipment that could provide accurate information beyond recreational limits, but simply doesn't for "legal" reasons. It probably makes sense to people - "oh they don't want to be liable for giving advice past recreational limits", but other companies seem to have navigated this legal issue and choose to provide accurate information regardless of this arbitrary limit.
As another commenter pointed out, I have no idea what it does past 130 feet, but the disclaimer that it _cannot_ be used past 130 feet, rather than one that says you _shouldn't_ use it past 130 feet, is somewhat concerning to me, even if I don't approach those limits.
I'm not assuming anything - and I'm not speaking as a pundit on Apple, I'm speaking as a consumer in the target audience with specific, important questions about a safety-critical piece of equipment. The answer to my question is not clear from this marketing release, and I'm simply saying that affects my likelihood to purchase.
Also, in the case of lack of evidence either way, assuming it would shit the bed is _definitely_ the right approach in diving.
Knowing the current state of software development and Apple's tendency to make pretty things on surface but that breaks down when you actually use it, I'd expect it to tell you you can swim as fast as possible to the surface without decompressing, even from 100m deep.
A) oxygen partial pressure with compressed air reaches 1.05atm, with 1.2-1.4atm posing a serious risk of oxygen-induced seizures (extremely dangerous)
B) nitrogen partial pressure becomes high enough that it becomes narcotic (every gas gets you high at enough pressure, even noble gasses).