To those who like to dive in Indonesia, here is a good thread to read:
Thanks for connecting up these threads!
One item that is strongly supported on that thread is a 'waterproof marine portable VHF radio'. This thread is much longer but this item hasn't had that much of an airing here, apart from mention that it was included in the now discontinued earlier version of the Nautilus (LifeLine or NLL).
'IyaDiver' has long been thinking about SAR requirements in remote parts of the world where the infrastructure is weak. From what I can tell he has had considerable personal experience on this matter and has been posting on this from as far back as 2012.
Given that in remote parts your best chance of a rescue is by the operator who put you in the water in the first place, after SMB, whistle/DiveAlert and mirror/torch I can see his logic in having a marine VHF radio as the next most useful item. [n.b., he does go on to describe and agree with the additional redundancy options of AIS/DSC devices and PLBs as the last resort.]
The idea is to travel with two of them. Dive with one in a depth-rated canister and give the other one to the boat crew member who is designated to pick you up (colourfully described as around his neck!). The Icom IC-M73 is favoured but each are around the price range of one MRG or PLB1. Ouch!
A possible cheaper option; applying the same principles that at the moment of surfacing you are likely around a one hour drift away from your boat, you can see it but they can't see/hear or are not looking for you; a pair of walkie-talkies could provide the same functionality before you drift too far away. A pair of Motorola TLKR40 two way radios retail at a tenth of the price (making a depth-rated canister the more expensive component). There are several models of these toys but even base models quote a ranges over 4km which takes you to the horizon when low in the water.
10 Best Waterproof Walkie Talkies in 2019 [Buying Guide]
The main consideration for these is that with AIS or PLB devices, fully accepting that these are last resort options, you are likely to be in for fairly long waits of several hours in the water. How frustrating when at the time you are thinking about deploying them, you can still see the rib or pickup boat!
A marine VHF radio does have an advantage that if you are not on a liveaboard in that remote place, but are shore-diving or with a shore based operator that uses small boats/ribs, these operators won't have an AIS MMSI number you enter into your MRG, and are likely to be communicating with their boats using VHF. If you trigger your AIS/DSC device you are requesting a rescue from another operator who might not be the closest to you.
A final thought/question for those of you running SAR scenarios in your minds: what factors would you take into consideration when deciding when to dump your weights? I am thinking, at the time you decide to trigger the AIS or PLB device; does that seem sensible?