My brother keeps his room like Fort Knox.
Fort Knox
idiomA place which is very difficult to get into.
Origin
disputed originNamed after Henry Knox, the Continental Army's chief of artillery during the American Revolution and the first United States Secretary of War.
The company security is like Fort Knox, so you need a special badge to enter the building.
With its biometric scanners and armed guards, the private research facility was effectively a modern-day Fort Knox, impenetrable to any unauthorized visitor.