Now Facebook is starting to test the ability to create one-to-one secret conversations in Messenger that will be end-to-end encrypted and which can only be read on one device of the person you’re communicating with. That means the messages are intended just for you and the other person — not anyone else, including Facebook. Within a secret conversation, you can also choose to set a timer to control the length of time each message you send remains visible within the conversation. Facebook's technology uses the Signal Protocol developed by Open Whisper Systems.
Starting a secret conversation with someone is optional. Secret conversations can only be read on one device. It’s also important to note that in secret conversations rich content like GIFs and videos is not supported, along with making payments, or other Messenger features - at least for now.
Secret conversations are available on a limited test basis right now, but Facebook will be making the option more widely available this summer.