Edit in JSFiddle

var HelloCtrl = function($scope) {
    $scope.name = '';
    $scope.$watch(function () {
        console.log('$watch expression is called!');
        return $scope.name;
    }, function (newValue, oldValue) {
        console.log('"name" changed: ' + oldValue + ' => ' + newValue);
    });
};

<div ng-app ng-controller="HelloCtrl">
    <label>Name:</label>
    <input type="text" ng-model="name" placeholder="Enter a name here" />
    <hr/>
    <h1>Hello {{name}}!</h1>
</div>