Good question. A conversation with my elderly aunt prompted the question. She told me that she took a bath and had trouble getting out. I first suggested a seat for the bath and also suggested she take the phone in the bath with her. That is when she said that the phone wouldn't do her any good that the doors were locked.
She has a granddaughter living with her so she doesn't live alone, but she was by herself when she couldn't get out of the bath.
I leave a key hidden outside. I have taken my car to the shop and left the house key on the key ring more than once. Hint. The key is not under the door mat.