In general, SOS is a Morse code signal used internationally to indicate distress. This was originally used for maritime industry. Now a days, we see the SOS as one of the feature in mobile devices such as smartphones and smartwatches.
To use the SOS feature user can set up a list of emergency contacts. Most of the mobile device vendors have this feature enabled on press of power button. In case of emergency situation, when power button is pressed continuously certain number of times, quick alert is sent to user’s contacts about the distress or panic.