The Turn-Key is different from a Double-Key Reversal in that it is a key reversal reversing a key reversal which has reversed a previous key reversal. Assume an uptrend and an initial downward reversal for the current discussion.
The Turn-Key Reversal carries much more weight if the fourth day also closes below (above) the third day's low (high) and/or the second day's close.
The pattern begins with a high above the previous day’s high and a close below the preceding day’s close (standard key reversal). The ensuing day trades below the second day’s low but reverses higher (alternating key reversal), ultimately settling for the day above the second day’s close, but not above the highest close.
The fourth (trigger) day exceeds the previous day’s high -- and often the second day’s high -- and closes below the previous day’s settlement price (third successive key reversal). The difference between a Double-Key Reversal and a Turn-Key Reversal is that in a Double-Key, both reversals are in the same direction whereas in a Turn-Key, the reversals are in alternating directions.
This pattern carries much more weight if the trigger (fourth) day also closes below the third day’s low (outside day reversal) and/or the second day’s close (two closes prior). The latter of these filters -- closing below the close of two days prior -- leads into a very effective short-term pattern (whether or not it occurs in the context of a Turn Key Reversal). It is called the 2-Close Reversal.