Example Umbraco property editor code for writing to the model.value and listening for changes without using an angular watcher

propeditor.js

//here we declare a special method which will be called 
// whenever the value has changed from the server
$scope.model.onValueChanged = function (newVal, oldVal) {
  // Model value changed so update UI
  updateUi()
};

var unsubscribe = $scope.$on("formSubmitting", function () {
  // Write data back to the model.value
  $scope.model.value = ...
});

$scope.$on('$destroy', function () {
  unsubscribe();
});