The old man at home can't hear clearly when knocking at the door outside. How to write a hint?

1. First, put a sign on or near the door, which says please knock loudly and speak loudly. Remind the knocker.

2. Secondly, write that the elderly at home can't hear clearly, and knock on the door if they can't hear clearly.

3. Finally, leave the old man's mobile phone contact information in case the visitor can't make a direct call when knocking at the door.