knockcode
nounUK /ˈnɒk.kəʊd/
US /ˈnɑːk.koʊd/
A knockcode is a secret pattern of knocks you tap to open something or show who you are.
She tapped the knockcode on the door so her friend knew it was her.
OTHER MEANINGS
2. A sequence of knocks used as a password to enter a club or secret meeting.
Only members who knew the knockcode were let into the treehouse.
3. A coded message sent by tapping knocks in a set rhythm.
The prisoners used a knockcode to talk through the wall.
4. A feature on some phones where you tap the screen in a pattern to unlock it.
He set a knockcode on his phone so no one else could open it.