The Armblade is a weapon that can only be used by races with the Living Construct racial feature, such as the warforged.
Armblade
Level 2+ Common
This serrated sword blade fits snugly over one of your arms.
Lvl 2: 520 gp Lvl 7: 2,600 gp Lvl 12: 13,000 gp Lvl 17: 65,000 gp Lvl 22: 325,000 gp Lvl 27: 1,625,000 gp
Weapon: Light Blade, Heavy Blade
Enhancement: Lvl 2: +1
Lvl 7: +2 Lvl 12: +3 Lvl 17: +4 Lvl 22: +5
Lvl 27: +6Critical: +1d6 damage per plus
Property: You gain a +2 item bonus to opportunity attacks with this weapon.
Special: You must have the living construct racial trait to use this item.