Morse code may not be used all that frequently in today’s era of Snapchat filters and Twitter outrages, but learning these three letters can still save your life.

S-O-S isn’t actually an acronym for anything, despite what your Sailor grandfather may have told you — it’s really just the letter designations for the string of dots and dashes that are universally recognized as a distress signal.

To broadcast SOS audibly (on a radio, using a whistle, or just banging rocks together) bang or beep three times in quick succession, three slow bangs or beeps, and then three more quick ones. In written form, it’d sound like beep-beep-beep…beep—beep—beep…beep-beep-beep.

To convey the same message using a signal mirror or light source, simply flick the light at those same intervals.