Health
From Halopedia, the Halo wiki
Health in the Halo games is the player-character's physical well-being. In the games, a player's health is measured and displayed on the heads-up display (HUD). If a player's health runs out, their character dies; however, lowered health does not affect a player-character's stamina, movement speed, or other physical attributes.
Appearances
Halo: Combat Evolved
Players in Halo: Combat Evolved have a limited, non-regenerating supply of health. Health can only be restored by picking up health packs. Health is shown on the HUD using a horizontal bar broken into ten segments. A player's health can only be reduced if their shields have failed.
In addition to being broken into segments, the health bar changes color to represent the approximate amount of health a player has left. The bar turns yellow when half or more of a player's health has been depleted; when this happens, the player should probably consider obtaining a health pack soon, though the need is not urgent. When only two segments remain on the bar, it will turn red, indicating that the player should find a health pack as soon as possible, and should avoid dangerous situations until then. When only one segment remains, the sound of a beating heart can be heard.
Halo 2
Contrary to popular belief, there is a small amount of health in Halo 2, though it is not explicitly shown on the HUD. Health recharges with a player's shields; this is canonically explained by the presence of biofoam injectors in the MJOLNIR armor that the Master Chief uses in this game. The shield bar appears to change color slightly to reflect the player's health.
Halo 3
The health system in Halo 3 is a bit more complicated. Bungie has stated that players have 115 hit points: 45 health points and 70 shield points. When a player's shields fail, their health becomes vulnerable. If the player avoids taking damage for 10 seconds, their health will slowly regenerate at a rate of 9 points per second. Health and shields are independent; a player's shields can regenerate without their health following suit, so full shields do not necessarily mean that a player is safe from death.[1]
Halo 3: ODST
In Halo 3: ODST, players once again have a health bar that is shown on the HUD[2]. A player's health in ODST can only be damaged after their stamina is depleted. Because players play as ODSTs (who are weaker than armored Spartans), health in this game is depleted much faster than in previous games of the series. As in Halo: Combat Evolved, health can only be restored using health packs.
Halo: Reach
In Halo: Reach, Spartans have limited regeneration. When a Spartan is damaged, after four seconds his health regenerates to the nearest third. If a Spartan is brought down to or below 2/3 health, the remaining health can only be restored by picking up a health pack, or, by using a Drop shield.
Elites cannot use health packs, but their health can regenerate completely, though more slowly than a Spartan's regeneration.
Gameplay
Health packs
Player's health can be fully replenished by obtaining a single health pack; this does not regenerate shields however. Health packs are only featured in Halo: Reach, Halo: Combat Evolved andHalo 3: ODST. They do not appear in Halo 2, Halo 3 and Halo 4.
Fall damage
In the campaign and multiplayer mode of Halo: Combat Evolved, Halo 3: ODST and Halo: Reach, players can take damage if they fall from too great a height. Such fall damage can kill players who fall from great heights. Fall damage is not present in either Halo 2's or Halo 3's campaign or multiplayer, however, though falling deaths can still result from contact with a kill barrier.
