Google Hangout's doesn't show if someone is online, so some of my contacts sometimes assume I'm online. How can I set an automated reply in Google Hangout like "I am not available on Hangout. Please send me an email instead."? I use Gtalk Autoreply for Gtalk.
You can use https://gchat.simon.codes to set up an automatic reply (disclosure: I made it) . It's intended for unused accounts though, so it might not be what you're looking for if you often log into the account.