Guard Nodes are robots that move very quickly around force fields, be it Green, Yellow, Purple, Orange or Blue, in various locations in the Alimbic Cluster. Depending on the color of the wall behind them, they must be hit with the weapon of the same color (i.e. Green ones must be hit with the Battlehammer). They are named in each force field scan. Attacking a guard node or force field with the incorrect weapon will result in the guard node firing back with the correct weapon.
They slightly resemble Airthorns.