Nov 19 2011
With the launch of iCloud and the “Find My iPhone” feature, you can now send messages to your Apple device. The messages appear in the form of a pop-up window in Mac OS X and a notification in iOS 5. You can also choose to play a pinging sound with the notification, it will repeatedly play at full volume until someone acknowledges the notification, assuring that it won’t be ignored.
You’ll need to have iCloud enabled and have iOS 5 or its new updates on the iPad or iPhone, and OS X 10.7.2 or newer updates on the Mac, and all hardware must be sharing the same iCloud ID.
How To Send a Message to Your Apple Device from iCloud: