I would highly recommend at least buying a cheaper secondary dive computer to take with you in case something goes wrong.

That’s standard diving practice. You have a backup regulator and a backup dice computer. And in the event of both primært and secondsry familier you have a plan for how to handle it.

But both the backup regulator and dice computer is on your companion. You don’t dive with two yourself.

> But both the backup regulator and dice computer is on your companion. You don’t dive with two yourself.

You're entirely welcome to have backups. I dive with 2 lights, and if the Apple Watch didn't require a subscription I'd gladly buy it to also dive with 2 computers. My divemaster had a second bottle with its own independent octopus for cave diving.

Anything you can afford to double (both financially and in terms of practicality/weight/encumbrance), by all means, go ahead and do it. Triple it if makes sense.

You don't dive with two regulators? I haven't been in a while but I fairly distinctly remember having two regulators per person, that way if one fails you don't have to immediately fall back on passing regulators back and forth breath-by-breath. The backup isn't a particularly nice regulator, probably reusing the mechanism your vest uses to inflate, but better than nothing.

Regulators come in two stages; you carry a backup second stage for someone else if their system fails - but you don’t carry two first stages (the part that screws onto the tank).

We do carry two first stages, but mostly only in colder water when there's a chance the first stage would freeze (water under 15C or so?) :)

You get air tanks that have 2 mounts for first stage and the octo goes into the separate first stage, giving you two independent setups.

I've only seen crazy swiss people do that though.

Wow - I stand corrected. That's super interesting. I am doing only tropical diving, preferably in a shortie!

In sidemount diving, each diver carries two completely independent tanks & regulators, one on each side of their body.

While it is used primarily in cave diving because it is more streamlined and less likely to collide with cave ceilings and features, I find it also quite comfortable for recreational dives with a pair of AL40s.

It’s also a fun conversation starter with other divers who are curious about my gear!

I would refuse to dive with anyone who isn't carrying two regulators. Sharing a respirator is feasible...but it requires practice to do well and significantly impairs your ability to move around or accomplish other tasks.

Backup dive computers are much less common and most people use their buddy as their backup computer. It is much safer to surface without a functioning dive computer than it is to surface without a functioning regulator.

Second stage is duplicated but the first stage is still a single point of failure. The backup for that is your buddy.

Which is precisely why I would refuse to dive with someone that doesn't carry two second stages.

I don't see the point of a backup dive computer for most people.

Every dive I've done has been on a boat with quite a few people all doing the same sites during the day. If your computer failed you can still estimate NDL from others on the boat and just err on the side of caution. Or even just rely on paper charts like people did for decades.

If you're doing cave diving then obviously a whole different story.

I agree, I don't know anyone offhand who uses two computers for recreational diving, and I would absolutely use an Apple watch as my sole dive computer. If you have a computer malfunction you can still safely return to the surface. The only reason to perhaps carry a backup is if you've traveled a long way or otherwise invested a lot of money in the trip.