In Harry Potter and the Order of the Phoenix, chapter 23 a healer uses Alohomora to open the door to the long term residents' ward:
The Healer pointed her wand at the door of the Janus Thickey Ward and muttered, 'Alohomora.' The door swung open and she led the way inside, keeping a firm grasp on Gilderoy's arm until she had settled him into an armchair beside his bed.
Alohomora is described as "the thief’s friend" at Pottermore and is clearly not a spell for a day-to-day tasks.
Why does she use Alohomora? She's not an outsider.