Facebook Legacy Contact - Facebook Security

[djone]

Hello Every One,

I have check my security settings for my facebook profile and I added my friend name into My Legacy Contact.
As per Facebook,"A legacy contact is someone you choose to manage your account after you pass away. They'll be able to do things like pin a post on your Timeline, respond to new friend requests, and update your profile picture. They won't post as you or see your messages."

I have read all guidelines for legacy contact but still I have confusion How Facebook will know that A person is just passed away? I read all information but still not getting what facebook want to say for Legacy Contact.

Can anyone knows how legacy contact works and how facebook will know that a person is passed away or not??