Are you allowed to touch an alarm clock on Shabbos?
You are allowed to touch an alarm clock on shabas. One may touch anything on shabas that one may touch during chol. (Rema O.C. 308:3)
As explained there, the prohibitions of Muktzah only apply to moving an object, not touching it.
R. Menashe Klein writes in Mishneh Halachos 11:304 that one is allowed to turn off the alarm on a mechanical alarm clock on Shabbos, even while the alarm is sounding. He writes that this is not a problem of "extinguishing", rather it is merely preventing the alarm from ringing more.
(In 13:49 he makes clear he is talking only about mechanical alarm clocks and not electronic ones -- but surprisingly enough there are plenty of wind-up alarm clocks still on the market nowadays)