A book about a kid who acquires a key that has notches on the end of it, when he turns the notches the key teeth rearrange allowing him to open any door.

[Austin]

I read this (I believe 3 book series) in middle which would have been around 2009-2011. I believe the book was some sort of spy related book involving a skeleton key. It s not Alex Rider Skeleton Key, this book is about a physical skeleton key. I don't remember much other than it was spy related and involved the key. I would give anything to know the name of this series again.