The DSC (Digital Selective Calling)  “panic button” is one of the more important safety innovations in the last few years. Pressing the button for 5 seconds will send an automated mayday call to all nearby DSC radios.   The mayday message will sound an alarm on other boat’s radio and then show the position of the distressed vessel. The mayday message will also interrupt any conversations occurring on any receiving radios.  The Coast Guard automatically sees and records the message.  The fact that the GPS coordinates do not have to be relayed over voice is quite an innovation.   There are also many times when the crew of a distressed vessel may not be able to spend a prolonged time on the radio.

Many boats do not have GPS data supplied to their  DSC VHF radio.  The wiring required to share the data between a GPS device and the VHF unit is fairly straightforward. The blog Aboard Astrea gives a simple primer on the subject here.

ICom has produced a short video explaining DSC.