Key for indicating whether the door is locked

The key is design for those people who has the habit of repeatedly checking the door after going out. The product allowed them to see the door locking status directly on the key, towards a pattern on the handle, instead of returning to the door from far away only for a check or feeling worry about the door for the rest of day. The function is achieved through a simple mechanical principle. The key is composed of two parts which can rotate relatively for a certain angle. While users turning the key to lock the door, an angular displacement will occur by the torsion. The pattern combined by two parts will be changed from “open lock” to “closed lock”.