A secret conversation in Facebook Messenger is end-to-end encrypted and intended just for you and the person you’re talking to.
When you send a message in a secret conversation, you can also set a timer to have your message disappear from the conversation. Your message will disappear in the amount of time you choose after the other person sees the message.
Keep in mind that you may be asked to turn on Secret Conversations in a new window. If this happens, tap 
Secret Conversations on the window to turn it on and then continue.
Start A Secret Conversation on Facebook Messenger:
In Android:
If you don’t see the option for disappearing conversations, try downloading the latest version of Facebook Messenger from the Play Store. Keep in mind that secret conversations aren’t available on Facebook Messenger Lite.
- From
Chats, tap
in the top right.
- Tap
in the top right.
- Select who you want to message.
- If you want, tap
in the text box and set a timer to make the messages disappear.
iPhone or iPad:
- From
in the top right.
- Tap Secret in the top right.
- Select who you want to message.
- If you want, tap
- Tap set a timer to make the messages disappear.
Secret conversations are currently only available in the Facebook Messenger app on iOS and Android, so they won’t appear on Facebook chat or messenger.com.