A Treasure Chest Unlocks with Whistles Converted into Japanese Characters
口笛が鍵になる宝箱｜しまちゃんと口笛海賊の秘宝 | ProtoPedia
A treasure chest project called 'Shimachan and the Whistling Pirates' Treasure' uses the pitch and number of whistles to encode Japanese syllables and enter a personal password. The design pairs the opening of a physical chest with lights and sounds. Its maker, @kuchibuekun3, lists Arduino among the hardware and currently marks the project as in development on ProtoPedia.
No key to carry around, but you have to whistle a little tune every time you want to open your treasure chest.