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Lock-On mod (known as the Seeker mod in Secret Agent Clank) was a mod that can be locked on to single target while strafing. It also showed the target's health. It should be noted that in the Vita versions of Going Commando and Up Your Arsenal, because the HUD is squeezed towards the center of the Vita screen the Lock-On Mod will no longer display an enemy's health.
In Size Matters and Secret Agent Clank, the Lock-On mod automatically locked on to enemies with no need for strafing, but it did not show the health of an enemy.