My Boat tracker alerts once it moves somthing like 100 meters from set location.
The only issue with these things is battery drain, a decent solar panel \ little wind turbine could quite happily keep it going.
I can also call it and it replies with an sms of its coordinates that has a link and will bring up a map on most smart phones.
But as I said, battery drain is the issue, esp if boat not used for long periods.
All the best Paul,
Rob