From the ETS Ultimate PLB FAQ at http://www.equipped.org/faq_plb/default.asp :

"Deliberate misuse or a transmitting a hoax distress is a federal felony punishable by a $250,000 fine, imprisonment for six years and restitution to the rescue agency for all costs incurred responding to the false distress."

Ouch! Accidental signaling is a different story. You can either contact officials to cancel any rescue activities ASAP, or at worst rescuers will be happy to find you alive and in no danger - but I'm sure there will be a LOT of questions to make sure it was truly an accident.

When you purchase a PLB your a required by U.S. law to register your beacon. The registration form requires you to provide telephone numbers for yourself and an emergency contact.

The rescue process involves calling the telephone numbers to determine if the PLB's owner could actually be in the place where the beacon reports AND be in need of rescue. If in doubt, a SAR team will be called into service.