Facebook announced today that it is adding new privacy and security features to Messenger, which includes an App Lock that uses biometric authentication, including Face ID or Touch ID, to unlock the app. This can be convenient, as you can let a friend borrow your unlocked phone, and not worry about them being able to access your Messenger chats. The feature is presently available on iOS, and Android users will receive it "in the next few months."
Another small change that's coming to Messenger is a new Privacy section, that lets users control features like App Lock and what users they've muted or blocked in one place. Messenger will also experiment with a feature that blurs images sent by users who aren't your Facebook friends since these are more likely to be inappropriate. This feature is already present on Facebook-owned Instagram and WhatsApp.
Facebook also stated that it will soon give users the ability to limit who can send them messages, so users can "decide who can message or call you directly, who goes to your requests folder, and who can’t message or call you at all." A similar message control feature is available on Instagram.