$window.alert not working inside angular function

I want to popup an alert message from an angularJS function, but it's not working.

Script

app.controller("APIController", function ($scope, $http) {
$scope.saveSubs = function () {
    var sub = {
        UserName: $scope.username,
        Password: $scope.password
    };
    if ($scope.username === 'admin' && $scope.password === 'admin') {
        window.location.href = '/Home/HotelSearchRedirect';
    } else {
        $window.alert("User name or password wrong. please enter correct username or password.");
    }
};});

What is wrong with this code?