Push Notifications

Push Notifications

Mobile

Note! If the user disable notifications and background refresh even silent notifications will not work
http://stackoverflow.com/questions/30644343/is-silent-remote-notifications-possible-if-user-has-disabled-push-for-the-app

Android
GCM has been replaced by FCM
https://firebase.google.com/docs/cloud-messaging/

Apple
https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/APNSOverview.html#//apple_ref/doc/uid/TP40008194-CH8-SW1

Web
https://developer.mozilla.org/en-US/docs/Web/API/Notification

Best solution
Sockets while the user is online.
Push Notification when the user is offline