See The Unseen

Warlock Invocation
Level: Least, 2nd lv.
Components: V, S
Casting Time: 1 standard action
Range: Self
Duration: 24 hours
Saving Throw: None
Spell Resistance: No

When you use this invocation, you can activate great powers of vision, allowing you to see invisible creatures and objects (as see invisibility). You also gain darkvision out to 60 feet for a period of 24 hours.

(Complete Arcane, Page 134)