Our valves are built to sense motion. Oftentimes gardeners, gates, children, etc. push or bump into the valve which accidentally causes them to go off. Make sure that a stabilizer bracket is installed to keep the valve in place and prevent such trips from occuring. Cars or people passing by without touching the valves should not cause them to go off.
If this is not the case, make sure that the valve is level within 2 degrees of the pipe. Unlevel installation can cause the valve to work improperly.