For years, I have used a SPOT Tracker when paddling by myself in remote areas which might not have cell coverage.
It lets me send pre-programmed text messages to family and friends, which I use to notify them when I start a trip, reach a waypoint, and when I end the trip.
They can also see my progress on a map, if they choose.
If I ever got in trouble, I would have the option of either alerting them, or alerting a search and rescue team (extra annual fee for the rescue team option).
I can customize the list of people to receive alerts, if desired.
I also have used it on long road trips, in my car, so those I select can monitor my progress.
There is no need to notify anyone ahead of time, when I get the urge to go paddling: I just use the Spot Tracker to notify them when I actually start the trip.
: )
There are also other GPS devices which do similar things (Garmin).