There are several ways, a pair of Moving Averages with small (you have to tell what small is for you) differences, Bollinger Bands narrowing for, say, two consecutive bars, no price movement over “n” pips for at least “x” bars….It’s up tou you to tell when a range is starting.

It’s a lot easier to spot it on a chart, especially when it ends!

This Nicolas‘post when, as a novice, I needed some help https://www.prorealcode.com/topic/detecting-a-range/#post-10338.

The following example uses narrowing Bollinger Bands for just 1 (or whatever number you want to set) bar.

First you have to define a BB:

// Set up a Bollinger Band
ONCE BBavg = 20                                        //20-period BB
ONCE BBdev = 2.0                                       //2.0 BB Deviation
BBmean = average[BBavg,0](close)                       //BB mean (middle line)
BollUP = BBmean + ((std[BBavg](close)) * BBdev)        //BB Upper Band
BollDN = BBmean - ((std[BBavg](close)) * BBdev)        //BB Lower Band

Then you have to determine when the BB starts narrowing,  because the price is likely to enter a range:

// Determine current status of BB (Narrowing)
ONCE NarrowingBars = 1     //You may want to change this to suit your needs
Narrow = (summation[NarrowingBars]((BollUP < BollUP[1]) AND (BollDN > BollDN[1])) = NarrowingBars)

Now you can use the variable NARROW to check whenever you want:

IF Your_Conditions AND not Narrow THEN....

I find the best practise is using highs and lows. By definition a trend can only exist (up) if prices are making higher highs and higher lows.