Some guy already made a health bar UI / HUD for in game. But if I'm being completely honest it's extremely clunky in every way possible. You never know WHO's health you are looking at when all the cops just get together in a cluster. In Hoxhud in PD2 the health popped up over each individual cops head rather than just the middle of your screen. I know this is easier said than done to add in the game but I guarantee the first person that does it will have the #1 PD3 mod on this workshop.