Was deliberately not quoting the exact reg so that the OP could do some reading for themselves, however,
2.2 IFR flights require the submission of comprehensive flight notification and the transmission of inflight progress reports at regular intervals. SARWATCH is based primarily on the receipt of these reports by ATS.
2.3 Pilots of VFR flights nominating a SARTIME to ATS, and those intending to operate in controlled airspace (except for VFR flights in Class E airspace) must submit flight details to ATS.
2.4 The order of preference for pilots to submit a comprehensive flight notification is:
a. via pilot access to NAIPS (via the Internet),
b. in writing,
c. by telephone, or
d. by radio to ATS.
Nb. Flight
details can be submitted in flight by alerting the controlling station with either "inbound details" or "transit details".