We'll watch your friends and alert you when someone unfriends you.
You don't have to worry about us notifying you any other way than email. Your friends won't know you're using this service unless you want them to.
When we've detected you've lost a friend we'll send you an email showing you who unfriended you.
Sign up and forget about it - we'll only contact you when there's a change in your friends.
We'll never sell your data. We won't spam you. Your email is safe.
We've never seen a Facebook app that can tell you retroactively who's unfriended you. Only after the point you grant the app permission to access your friend list.