I have used following code to reply fixed text as SMS programmatically and is working fine. Similarly I want to reply a fixed text to hangout programmatically without any user interaction
SmsManager.getDefault().getDefault().sendTextMessage(phoneNumber, null, msg, null, null);
You can reply to Hangout SMS but not Ping. Hangout doesn't expose email address of all contacts in Notification, and It has no API exposed till to reply hangout ping. So for third party application there is no way.