Here's a real wild alarm clock.  The shelf was not only optional, it was fake.  By that, I mean the shelf didn't support the clock--it was vice-versa.  The clock has a nail hole slot in the back like a kitchen clock.  The shelf attached to the bottom by means of a couple of expandable pins.  The movement was the same as in a clock radio.  Pull the knob out to arm the alarm, in to shut it off.  The other you pull out to set the time, push in to set the alarm.  If you didn't like the shelf, you could just leave it off.