So, I just got an Oceanic Pro Plus 2.1 integrated air dive computer. I've read some people bring backup devices with them. Is that really necessary? Do these things fail? Advice would be great!
And, the advice will be divergent.
AI computers and transmitters rarely 'fail'. That doesn't mean that they do not ever fail, only that it is uncommon to occur, during a dive. However, a few units may lose synchronization during a dive - in some cases the link is restored, in others it is not. Some transmiitters may 'fail' - stop transmitting - at lower pressures, but that is usually below 1000psi, or probably lower than 700psi.
As you can already discern from responses, some divers employ a 'hosed' SPG as a back-up, or rather as a primary. I do. My primary pressure gauge is my SPG. My AI computer / transmitter is a convenience, allowing me to check pressures by merely rotating my wrist to look at my computer during the dive, rather than unclipping my SPG from a waist D-ring. So, is it
necessary to bring a back-up device? My answer is 'No'. Yes, my computer / transmitter serves as a back-up, but it is brought for covenience, not necessity. If my computer - transmitter link fails, I DO NOT thumb the dive - I have the SPG. If my SPG fails during a dive, I call the dive.
An argument made by some in favor of using only the wireless AI configuration is that it improves the 'streamining' of gear. I have difficulty believing that the majority of divers who use a wireless AI rig can objectively discern any difference in the performance of their rig based on the absence of a single (high pressure) hose. Now, if the argument is that the wireless / hoseless AI set-up is more streamlined than a rig with an excessively large console, positioned at the end of an unnecessarily long HP hose, all inadequately attached to (and therefore dangling from) the BCD, I can readily see the argument. Of course, the logical solution in that case is a more streamlined SPG configuration.
It is worth adding that SPGs also fail, but also rarely, and it is also quite uncommon for an SPG failure to occur, during a dive. A couple of recent posts on SB attempted to quantify the relative frequency of failure of SPGs and wireless AI computers, to the end of suggesting greater reliability of wireless AI units. But, computation of valid, objective, comparative reliability data cannot easily be done. The preponderance of divers use a SPG, and notwithstanding the proclamations of reliability of wireless AI units, most reports of failure of equipment are anecdotal.