A basic concept in most rescue diver courses is self rescue to keep your self from being lost at sea dive, training is important but should it happen having 4 pieces of scuba diving equipment with you will make you chances of being rescued significantly higher and they are useful tools on most adventure scuba diving trips. Like the Boy Scouts say be prepared!
Plastic Whistles, Safety Sausages, Snorkels and a Light.
The 4 best things to have are a loud plastic whistle, a long safety sausage, a snorkel and a light. The good thing is this dive equipment will all fit in a dive pocket quite easily, and are relatively cheap dive gear to buy, so there is no reason not to have them.
Plastic whistles
Plastic whistles don't rust and they don't run out of air to sound them until it becomes moot. Sound carries a real long way on the water, especially at night. Most modern "BCD's" Buoyancy Control Devices have one built in, usually attached to the low pressure inflator, right next to where your mouth is. Another option is air powered horns also attached to the low pressure inflator mechanism in a variety of ways. Air horns are even better at producing signal, put are not fool proof as they are mechanical and can have any number of things make them non-operational, and you will eventually run out of tank pressure to sound them. 50 bar of air will give you a lot of bursts, but as the pressure in the tank decreases, so does the volume.
Safety Sausages
Safety sausages are mostly orange with some being yellow. Searchers can spot these on the surface from a long way off for 2 reasons, one they are orange which instinct makes you pay attention to as it is usually associated with danger in the wild. The 2nd reason is that they are out of the water, in the air, and can be made to wave which further increases there visibility; again humans are hard wired in our reptilian brains to see things that move for food and safety. The main draw back is that they can not be seen at night unless, they are illuminated some how. As they have no movable parts or batteries they are Kiss simple provided they don't have a leak, and even with a leak they will float so can still be seen from the air, or decks on boats that are elevated. It also a good idea as a diver to mark where you are coming up at so boats doesn't run over you. Many safety sausages will also have a plastic whistle attached to sleeve that stores them, a good feature to look for when you are shopping for dive gear.
Snorkels
You want to get me worked up try telling me why you are such a pro that you don't need a snorkel! What a load of smelly poop, with the exceptions of night manta dives, or penetration dives on silt layered wrecks or caves, I always have my snorkel attached to my mask! I have been in flat seas more than once with no wind, and came up with a thunderstorm that was over the horizon at the start of dive, whipping up 2.5 meter seas in 45 minutes. If you come up away from the boat or the boat can't see more than 100 meters, you could be in for an exhausting 20 minutes or more fighting for breathe while swallowing and puking Neptune tea.
A Pocket Light
A LED pocket light is very handy for looking in holes in the day time for pipe fish and crabs and nudibrachs. I am especially drawn to extended battery life that the LED's provide, most go almost 8 hours before you need to change the battery, this could be the difference that gets you found if you are a drift on the open ocean at night. They can be used in a couple of ways, placed inside the safety sausage which will stand out as a beacon for a long way at night, again elevated, moving and out of place will get it seen. The 2nd way is to point it at boats, planes and helicopters and do the classic SOS, Save Our Souls, 3 long, 3 short, 3 long. Remember do this by moving your hand over the lens, not by turning the switch on and off which heightens the possibility of an equipment failure when you need it least.
Military, rescuers and commercial vessels, including high flying commercial flights will all respond to an SOS if they see it, if fact, are required by maritime law and tradition to respond if it does not put them or their ships in danger. With the long burn time of a LED you should get one maybe even two nights or more out of the batteries. A light turned on pointing at a boat in the day time can be seen for a long way off, and when the batteries die you can use it as a mirror in the day time to flash people a long way off to bring attention to you including planes and helicopters.
As usual the best defense is a good offence, keep the software in your head engaged, stay within your dive abilities and training, be aware of strong currents, monitor local weather forecasts, keep your dive gear in good order and plan your dive and dive your plan . These will always be your best bet from being Lost at Sea.
