How Apple could fix iMessage notifications across devices
Apple recently released a beta version of Messages for OS X, as part of the unveiling of the preview of Mountain Lion. While I think most people are happy to have the ability to send iMessage messages from their computer to their contacts that are on phones or iPads, one universal complaint I’ve heard is that if you have multiple devices with Messages on them, for example a Mac, an iPhone, and an iPad, you get notifications of incoming messages on all of them. For. Every. Incoming. Message.
Apple does go so far as to mark messages read on the other devices once they’re read on one device, but it’s much harder to solve the notification problem since there’s no reliable way to know which device the user happens to be using.
But I have a proposal that I think would help the situation a lot.
What if iMessage (the service) tracked the last device the user used, and delivered any incoming messages to it first. Then, if after a 10 or 15 second delay the message had not been read, the message gets delivered to all of the user’s other iMessage devices.
In practice this would mean that new messages would most often get delivered to all devices, but once a conversation started on a given device, the extra notifications on the other devices would stop. Further, the user could still feel confident walking away from one device and carrying on the conversation on another device, with the worst-case scenario being that a single message could be delayed by at most 15 seconds at the time of the device switch.

