May one set an alarm erev shabbos for shabbos morning and it will be going off the entire shabbos. (Agav there’s no issue with putting a towel on it to block the noise or there is)
You are allowed to set an alarm on erev shabbos even though it will ring on shabos itself. This is because you didn’t do any melacha on shabbos, and it is known that it was set from before shabbos. It is preferable that the alarm be in a place that you will not accidentily turn it off on shabbos when it rings.
Be’er Moshe 7 Kunt. Electric 47, Oz Nidberu 8-26.