Help key / key

Theory of the design:
This is a key with a small plate inside that can be retractile to tell people whether he or she locks a door or not.
It is usually that people forget to do or doing something, especially something trivial, such as lock a door. People often forget whether he or she has locked a door when going out. This key is designed to solve this problem. Based on keys we commonly use, this key is added the setting of a small plate inside that can be retractile.