"One day, Ali Baba is at work collecting and cutting firewood in the forest, when he happens to overhear a group of 40 thieves visiting their stored treasure. Their treasure is in a cave, the mouth of which is sealed by a huge rock. It opens on the magic words "open sesame" and seals itself on the words "close sesame". When the thieves are gone, Ali Baba enters the cave himself and takes a single bag of gold coins home."
Some other links to similar projects.
https://www.instructables.com/id/Secret-Knock-Detecting-Door...
https://hackaday.com/2020/05/25/secret-knock-unlocks-door/