that's an internal temperature monitor that detects when the helmet is getting too stuffy and activates fans to help cool the ...

power armor enhances strength, protection, and abilities. Armor has only recently become a prevalent part of modern warfare, with Chestplates and helmets being standard issue for most militaries ...

while other high-ranking Adeptus Astartes were usually given pieces of the Power Armor. Luckily, it's possible to get the Mk VIII Errant Helmet in Warhammer 40k Space Marine 2 for free ...