The arrows, and line can be turned on and off.
You can change the 50% to say 45% so that you will be alerted before it actually hits the 50% retracement.
The script will only alert if the reversal is a 2up red candle, a 2up green candle which will hopefully turn into a 3 candle.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.