I have a situation where I want my computer in my local network to send a notification (push notification, SMS or whatever) to either an IOS of Android device that is on this same LAN. The trick is that I want to send this notification only when the LAN connection to the internet goes down. This means of course that my LAN cannot communicate with email servers, it cannot communicate with any APNs or GCMs, etc.
Is there any way to do this? My computer (the sender) is a Linux box and it will know the local IP addresses for any IOS or Android devices locally.