In a nutshell: airplane mode
Turn off your data/wifi, read it, exit the app, and then turn data/wifi back on. This allows you to read it without it showing the read notification apparently. But I would test it with a friend just to be sure.
- Is it possible to turn off read receipts in Kakaotalk? : korea
I thought this was pretty clever. I like this because it's simple and doesn't need any extra apps.
Testing it out
I also took his advice and tested it with a friend. We put our phones side-by-side. He sent me a few texts (let's call them ABC), then I went to airplane mode, then read ABC inside the chat room. I then exited the app and turned off airplane mode. In fact, I then opened KakaoTalk (another chatroom, not my friend's chatroom) and was able to read other messages from others. My friend's phone still showed the messages as unread. Success!
Just to push the limits, I then exited the app again, and my friend sent another set of messages (let's call them DEF). I re-entered airplane mode, entered the chatroom, and read DEF. Exit the chatroom, disable airplane mode. Fully back online again. Friend's phone still showed all messages (ABC DEF) as unread. Nice.
So it seems that as long as you never enter that specific chat room while internet connected, you can get away with sneaky readings.
Just don't share this post with your boss.