Push notification is the delivery of information from a software application to a mobile-computing device without a specific request from the client. Push notifications generally originate from a server which can be either transactional or periodical.  Typically, the end user must opt-in to receive alerts; opt-in usually takes place during the install process and end users are provided with a way to manage alerts if they change their minds later on. To receive a push notification, the application for which the push-notification is sent need not be in active state on a mobile device. Different devices and services rely on different methods to deliver push notifications. Apple developers, for example, can use the Apple Push Notification Service's Developers application programming interface (APIs) to have their apps deliver push notifications to iOS devices. Another approach is to use mobile backend as a service (mobile BaaS) cloud services to provide push notification functionality for a mobile app.