They are similar to Lightning Spires from the second game; immobile charged orbs. Whenever a player comes within 30 yards, they release several chain lightnings, dealing Lightning damage to any target, enemy or ally, in vicinity. They are technically enemies (count as Ancient Ordnance type), and even grant experience when destroyed, but drop no loot and are overall more of traps than monsters.
The damage they deal is below average, yet they can make fighting other enemies in the area more complicated, especially in dense corridors of Pandemonium Fortress.
The design of Shock Towers implies that they are of angelic origin.