Key reminder / keyhole

Door-key is an item people use everyday.  A tiny thing controls the safety of the entire family.  Sometimes, due to carelessness, we left the key in the lock which would increase the risk of being robbed.  From the Physics experiment, I came up with the "Key Reminder" idea.  By placing a device called "photoelectric timer" in the seat of keyhole, and using infrared rays as detecting tool.  When a key is left in the keyhole, the device will produce "Bi" sounds and red light continuously to remind people.  The "Key Reminder" can help people to avoid the situation of leaving the key behind.