On The Big Bang Theory
As an adult, Sheldon Cooper has a ritualistic knock that he uses whenever he's knocking on somebody's door. As established on The Big Bang Theory, Sheldon knocks three times then says the person's name and he typically performs this three times.
Learn more about Sheldon's knock on The Big Bang Theory
On Young Sheldon
Sheldon has not yet fully developed his later knocking pattern. In its embryonic form, Sheldon still knocks three times and calls out the person's name, but he doesn't yet do this in triplicate.
Sheldon's knock was first seen in the episode "A Patch, a Modem, and a Zantac", when Sheldon visited Meemaw's house to ask for money to buy a computer. He knocked three times and said Meemaw, but he only did this once.
The knocking ritual was extended to two rounds in "An Eagle Feather, a String Bean, and an Eskimo", as Sheldon visited Meemaw to show off the uniform for his new school. Sheldon stuck with two rounds when he visited Meemaw in "Summer Sausage, a Pocket Poncho, and Tony Danza" to ask her about her date with Dr. John Sturgis.
When Sheldon woke Georgie up for help with his paper route in "A High-Pitched Buzz and Training Wheels", he performed two rounds of his knock on Georgie's headboard. Sheldon again stuck with two rounds when he knocked on Georgie's bedroom door to prank him in "A Stunted Childhood and a Can of Fancy Mixed Nuts".
This page has been updated up to episode 210 A Stunted Childhood and a Can of Fancy Mixed Nuts
Featured in these episodes:
When Sheldon goes to Meemaw's house to ask for money for a computer, he knocks on her door with a minimalist version of his ritual knock. Sheldon knocks three times and calls for Meemaw, but he only does one round of this.
When Sheldon goes to Meemaw's house to show off his new school uniform, he knocks on her door with his characteristic knock. He knocks three times and calls Meemaw's name, and he does two rounds of this.
When Sheldon goes to Meemaw's house to ask about her date with Dr. John Sturgis, he performs his characteristic knock on her front door. Sheldon knocks three times and calls out for Meemaw, and he does two rounds of this.
After Sheldon gets up on his first day as a paperboy, he goes to his brother's room and knocks on Georgie's headboard to wake him up. Sheldon knocks three times and says Georgie's name, doing this twice.
When Sheldon goes to prank Georgie with a can of "fancy mixed nuts", he knocks on Georgie's bedroom door. He performs two rounds of "[knock] [knock] [knock] Georgie!"
When Sheldon goes to Georgie's bedroom to see Veronica, he knocks on the door. As he has always done on Young Sheldon, he only performs two rounds of "[knock] [knock] [knock] name".
Season 4, Episode 01 - Graduation
When Sheldon goes to his parents' bedroom to tell them about his decision to attend college, he knocks three times and says "Mom?", and then knocks three times and says "Dad?".
When Sheldon checks for Dr. Linkletter in the men's room, he knocks three times on a stall before asking for Linkletter, although he only does this once.