There is a “Lock message” option in the Android Messaging app when you tap and hold any individual SMS text message. Users sometimes wonder what it means to lock a message. So what is it and what does it do?
The Lock message option makes the message where it cannot be deleted when you mass delete messages. This can be confusing for some, since you can still tap and hold the message and select Delete even when it’s locked. The purpose of this functionality tough is to prevent the message from being removed when you delete entire threads.
You’ll see this in action when you tap and hold an entire message thread and select Delete thread. There’s an option where you can choose Delete locked messages if you want to. Otherwise, the locked messages are preserved.