Richard Donchian, no longer with us, was the devisor of several trend-following systems, not least the Turtle Trading system, which is still with us.

Donchian channels are a measure of market volatility, much the same as Bollinger bands
and are about as simple as you can get:-

Take the highest period maximum and the lowest period minimum for last n periods, and produce an area. So, a stable price over preceding period will squeeze the Donchian channel, a more volatile price range will expand it.

Never much used in forex trading, and why, when Bollinger bands have superseded this approach…

Download the indicator:- donchian_channels