Why the Locking Buttons? (Project for blind user)
Locking button remains depresses.  This gives a blind person an ability to sense by touch, if some feature (which, perhaps, doesn't manifest itself by sound) is on or off.  Alarm clock would be an example of such feature.  If it were a momentary button, then it would feel the same whether the feature is on or off.

Lever switches, rocker switches, etc is another way of allowing the blind user to sense by touch if something is on or off.