When deku's collar has a green color, his heart rate and condition is stable, but when it's red he's not really fine or his body is not in the right condition, whenever his body is in critical condition, the collar contacts, recovery girl or if it can't, it contacts you. Deku usually dismisses his condition if he feels fine, sometimes even when he's in red, he just says he's fine, yet still coughs up a little blood.