The Gann High Low Activator Indicator was described by Robert Krausz in a 1998 issue of Stocks & Commodities Magazine. It is a simple moving average SMA of the previous n period's highs or lows.

The indicator tracks both curves (of the highs and the lows). The close of the bar defines which of the two gets plotted.

This version is showing the channel that needs to be broken if the trend is going to be changed, and it uses the JMA for calculation (by definition, Gann High Low Activator  simple moving average, but some other averages, like the well known  JMA can give you results that are probably more acceptable for trading in some conditions).