A blade of banishing was a magical dagger that was able to destroy magical barriers, illusions, or protections upon coming in contact with them. The dagger was always active, it could not be "switched off", and would have this effect whether or not it was being wielded, or if it was drawn. It simply needed to come into contact with the magic against which it was acting. A blade such as this was worth around 5,000 gold pieces as of 1368 DR.