RTF (Read The FAQ):
The Use Magic Device skill is for using magic items that
you normally could not otherwise activate. Activating a wand
has a DC of 20, as shown on the table in the Use Magic Device
skill description. However, this assumes that you already know
what spell the wand stores. If you don’t, you have to activate
the wand blindly (DC 25). If you successfully activate a wand
blindly, you know what spell it contains, and your subsequent
attempts to activate that particular wand are at DC 20.
There’s no arcane spell failure chance for activating a spell
trigger item, for a command word item, or for a use-activated
item. There is an arcane spell failure chance for activating a
scroll (a spell completion item), provided the spell stored on the
scroll has a somatic component.