Hard isn't the right word - it seems to not currently be officially possible. There is no documented interface for communication with users on Hangouts. Not e

Hard isn't the right word - it seems to not currently be officially possible. There is no documented interface for communication with users on Hangouts. Not even XMPP is supposed to work, though I and some other users are still able to use it. The only API available is for building applications that interact with the existing Hangouts UI.