How did sailors send distress signals before the invention of electricity?

There are few experiences which would be scarier than being stranded in the middle of the ocean, even on a boat equipped with electrical devices you could use to signal for help, such as satellite phones. One can only imagine how scary it would have been to be stranded without such luxuries.

Prior to the invention of electrical devices, stranded sailors would have to resort to primitive measures to signal for help. They could start fires on the deck to try to arouse the attention of nearby ships. During the daytime, other ships might see the smoke; during the night, they might see the light from the fire. If starting a fire was not feasible--if they were on a lifeboat, for instance--they could use a mirror to reflect light and catch the attention of any nearby ships. If they were lucky, they might also have a flare gun, which they could use to catch the attention of ships a bit farther away. Nevertheless, their chances of rescue remained dim.