How to identify a Bollinger Band Squeeze depends on the definition. Most of the people providing a definition have defined it as the net Bollinger Bandwidth being less than 6% of the centerline (they also usually specify a Period of 20 and a Std Dev setting of 2.00).

The best way to do this is to add Bollinger Bandwidth to the Charts and click on the BB to select Create Scan Condition | Less Than: .06

A Condition created this way is both easier to create and far more efficient than creating a Condition Formula. It will use fewer resources and calculate more quickly.

If you really need a Condition Formula instead, a Condition Formula for the 20-Period Simple Bollinger Band being less than 6% of the centerline could be written as:

4 * SQR(ABS(C ^ 2 + C1 ^ 2 + C2 ^ 2 + C3 ^ 2 + C4 ^ 2 + C5 ^ 2 + C6 ^ 2 + C7 ^ 2 + C8 ^ 2 + C9 ^ 2 + C10 ^ 2 + C11 ^ 2 + C12 ^ 2 + C13 ^ 2 + C14 ^ 2 + C15 ^ 2 + C16 ^ 2 + C17 ^ 2 + C18 ^ 2 + C19 ^ 2 - 20 * AVGC20 ^ 2) / 20) / AVGC20 < .06

Another possibility is that you want the Bollinger Bands to be decreasing in width for at least a certain number of bars. We can do this by creating a Condition Formula for the 20-Period Simple Bollinger Bands to be decreasing in width from one bar to the next:

ABS(C ^ 2 + C1 ^ 2 + C2 ^ 2 + C3 ^ 2 + C4 ^ 2 + C5 ^ 2 + C6 ^ 2 + C7 ^ 2 + C8 ^ 2 + C9 ^ 2 + C10 ^ 2 + C11 ^ 2 + C12 ^ 2 + C13 ^ 2 + C14 ^ 2 + C15 ^ 2 + C16 ^ 2 + C17 ^ 2 + C18 ^ 2 + C19 ^ 2 - 20 * AVGC20 ^ 2) < ABS(C1 ^ 2 + C2 ^ 2 + C3 ^ 2 + C4 ^ 2 + C5 ^ 2 + C6 ^ 2 + C7 ^ 2 + C8 ^ 2 + C9 ^ 2 + C10 ^ 2 + C11 ^ 2 + C12 ^ 2 + C13 ^ 2 + C14 ^ 2 + C15 ^ 2 + C16 ^ 2 + C17 ^ 2 + C18 ^ 2 + C19 ^ 2 + C20 ^ 2 - 20 * AVGC20.1 ^ 2)

And then using it as the Boolean Indicator in a Custom PCF % True with the Period set to the number of bars over which you wish to test and the Average Type set to Simple. You would then click on the Custom PCF % True Indicator and select Create Scan Condition | Greater Than: 99.9.

Creating Conditions from Your Chart