I believe this is an immature Centruroides exilicauda, or AZ bark scorpion. These scorpions are common here. I would prefer they stay outside, but I find many of them inside my house, especially during our summer monsoon season. I suspect this is a bark scorpion because it climbs and can lie with its tail sideways, more typical of this species -- I have been told that this species can make itself as flat as a credit card, so even if I didn't have a gappy house, they could still get in. Although the sting is potentially fatal, Arizona Southern University has reported no fatal cases of a scorpion sting in over 30 years -- I hope I don't break their record.