I opened a suggestion for this...
github.com/Scirra/Construct-feature-requests/issues/618
I think to recreate would be something like (I typed that without testing or anything)
if (speed != 0 && trackingVar === false) {
// on moved trigger function here
trackingVar = true
} else if (speed === 0 && trackingVar === true) {
// on stopped function (optional)
trackingVar = false
}