This Elite Security guard is armored.

The corps are now issuing high-tension personal armor to their security forces as standard equipment. I think they're getting scared of us. It would be flattering if it didn't represent an existential threat. Make sure you bring along something extra pointy for emergencies.
—Central

Many guards have armor, which prevents some attacks against them.

All attacks that can deal KO or lethal damage have an armor piercing value. If a guard has more armor than an attack's armor piercing value, then the attack is prevented against the guard. Buttons to attack guards that are too armored to attack will appear but be disabled, and “ARMORED” will appear when these buttons are hovered over.

Each guard type has an inherent armor value. This value can be increased by the Chiton daemon, and reduced by the Aces program.

Ways to KO or kill guards that do not involve direct attacks, such as Shock Traps, Laser Panels, Flash Grenades, and Flash Packs, are not affected by armor.