Locking our doors as we leave our homes has become such an integral part of life that we do it without much thought. One side effect of this banal routine is that it’s not uncommon for a person to question whether or not they locked their door. The act is so familiar and so forgettable that it’s hard to sometimes remember. Hence, this materials-driven study uses color-changing smart materials in a new kind of key that provides peace of mind.

The ChromiKEY looks like a typical door key, but it changes color when you turn it to lock your door. The smart key will stay that locked-in color until you use it to unlock the door again. Unlocking the door will cause the key to return to its original color. Hence, if your memory lapses, at any point, just look at the color of your ChromiKEY … its color will indicate whether or not your door is locked!

ChromiKEY achieves this by incorporating Elastink into the bow (or head) of the key. The smart material consists of photonic crystals that change color under pressure. Turning the key in the flange of the lock generates pressure in the threaded shoulder of the key; that pressure is transferred to the bow, thereby causing the bow to change color.

The project started off with the idea that a simple house key might indicate whether or not you locked your door, but it quickly unlocked other opportunities as well. The concept would work well for cars and vehicles, boats, storage lockers, mailboxes, and other lockable things. ChromiKEY would clearly indicate that your friend locked your place, which would be reassuring when they return your key to you. Its uses are wide open!