After progressing in the main quest to anger Satan enough, these distractions will appear in Hell. They are sort of like anti-air turrets that will shoot missiles at you whenever you are in their range. There’s a total of 26 in the game and you destroy them by just going up to them, holding the button shown until the meter fills.
Each Spire is guarded by a few demons, but nothing difficult at all. Note that you will want to shoot down a missile while hovering in the air (upgrade is purchasable in the Arcane menu) to earn the Top Gunner trophy/achievement . Make sure you do this before getting rid of them all.