Why won't focus sash work for my pokemon?

Question

every time a pokemon attacks the pokemon i have using focus sash at that time, the focus sash never kicks in when they get knocked out, isnt it supposed to leave me with one hp, same with my focus band

be specific, best answer gets the best answer award

Answer 1

focus sash only works if your pokemon's hp is full and its hit by a move that would knock it out in one hit, however for focus band it works some of the time