On one shoulder, I have a nice money savings conscience...on the other is the SMC forums!
So I went back today to see if the clock had the key, and sure enough it was in the locked case next to it. I tested it out with a dime and the alarm came on when the clock hit the right time, had to buy it at that point!
Pretty neat little item, very simple device to accept the dime, it simply moves aside a small lever that allows the plunger to pull up and set the alarm. Nothing there to reject slugs, not that people were looking to trick a $.10 item to wake them up in the morning.
I'll see if I can get a video of it working. The clock face has a small amount of grime on the inside around 8 o'clock, but it should just pull off so I can clean it.