Don’t you hate it when you can’t remember if you locked the front door when you last left your home? It’s a dreadful feeling that you don’t have to experience again thanks to a cool little accessory called CheckKEY.

Developed by Japanese lock manufacturer company Miwa, the ChecKEY is a sleeve-like accessory that goes over the top part of your regular key and features a small window that indicates whether you locked your door or not. The ChecKEY comes with a built-in mechanism that detects when you turn the key clockwise or counterclockwise and changes color accordingly. When you turn the key into a lock clockwise, the little window on the ChecKEY turns white, and when you turn it counterclockwise, it turns orange. The mechanism is entirely mechanical, so it never runs out of batteries. This way, when in doubt, you can just look at your key and tell if you really locked your door on your way out.