"The Silent Timer" sucks. Don't buy it. It's TERRIBLE. Mainly, it's the buttons. The buttons are rubbery and squishy. Several times, during proctored tests at Princeton Review, I kept pressing the buttons to reset the timer for the next section and the rubbery button would just squish left or right and never make 'contact' w/ the circuits below to actually reset the timer. I had to keep saying to the proctor "No No No - Do not start yet!".
Buy any other timer with nice buttons that actually work. Then just open it up and cut the 'noise' wire. I went to radio shack and bought mine. It wasn't silent but the salesguy cut the 'noise' wire for me.