Construct Lock

 
Prerequisite(s): Warforged, Base Attack Bonus 2+
 
Benefit: You gain a +2 bonus on damage rolls against creatures with the construct type. If you roll a critical threat against a construct, you can forego the confirmation roll and make aother attack using the same modifier. If this second attack also hits and you deal at least 1 point of damage, the construct must make a Fortitude check vs DC = 10 + 1/2 Char level + Con modifier, or be rendered immobile and helpless for one round. If you spend an action point to improve an attack roll against a construct and hit with the attack, the attack roll is automatically considered to be a critical threat regardless of the number.
 
Source: Races of Eberron