Knock three times

Knock three times can refer to:
 * "Knock Three Times", a 1970 song by Tony Orlando and Dawn
 * Knock Three Times (album), a 1971 album by Billy "Crash" Craddock
 * Knock Three Times, a 1917 novel by Marion St. John Webb
 * Knock Three Times, a 1968 British television serial that featured Hattie Jacques
 * A tap code or secret knock