An inadvertently-triggered PLB in New Zealand had rescuers coming to the rescue, because the boaters had not activated their radio or cell phones.
The family had registered their beacon and advised they would be wearing their lifejackets, but were unreachable when it accidentally went off.
It is important to register your beacon and also to keep the lines of communication open and stay vigilant, because help may be coming or might even be needed by another boat in your area.
Read more here:
http://www.scoop.co.nz/stories/AK1604/S00423/everything-done-right-except-turning-comms-equipment-on.htm