The SystemTrigger allows you to run your background task when a certain event occurs. This is different from a trigger that latches and waits for a condition because the SystemTrigger will latch immediately when the event specified in the SystemTriggerType is generated by the system. Certain events require the app to be configured for the lock screen. These apps must request lock screen access to use the trigger type. Other events can be used by apps without being placed on the lock screen. The list of triggers is available online at http://bit.ly/1q9jK2X.
It’s important to note the events are fired based on state changes rather than time intervals. For example, the InternetAvailable event is triggered when the system is first able to reach the Internet. This event will not trigger again unless the Internet is no longer available. After the Internet connection is lost, the trigger will fire again once connectivity is restored.