Church Tackle's Double Action Flag System is great for light striking fish. The flag can be adjusted for different lures and speeds by simply clicking the adjustment lever up or down. You can set the kit to provide a flag up or down to signal a fish strike. Easy to install and use. The Double Action Flag is not recommended for use with copper lines.
Installation video: https://www.youtube.com/watch?v=NOkd9sUsCu0&t=165s
Mark Martin explains: https://www.youtube.com/watch?v=UEJwp8qPV7U&t=21s