Alarm Clock on Shabbos: Avsha Milsa

My friend told me I can't have an alarm clock ring on Shabbat due to something called "Avsha Milsa" What is this. Is this true?

Shalom!

Thank you for your question.

The term “avsha milsa” refers to the ban on allowing noisy appliances to run on Shabbos. This is true whether it is an appliance turned on by means of a timer on Shabbos or whether the appliance was already on before Shabbos began. The ban of avsha milsa was enacted to ensure that a peaceful and serene atmosphere prevails on Shabbos.

The origins of avsha milsa can be found in a Talmudic passage that discusses the permissibility of operating a wheat grinder shortly before Shabbos and allowing it to continue grinding after Shabbos has begun. According to one opinion, it is perfectly permissible to do so but according to another opinion it is forbidden due to the noise it produces and the concern that people might suspect one of breaking Shabbos.

The first opinion is common among Sefardim and therefore they are permitted to operate household appliances that make noise on Shabbos. As such, a Sefardim are permitted to turn on the clothes dryer shortly before Shabbos and allow the machine to continue running on Shabbos even though it makes noise. Ashkenazim, however, follow the second opinion and generally forbid operating appliances on Shabbos that make noise.  

It is permitted, however, to set an alarm clock to wake one up on Shabbos morning. One reason for this is that alarm clocks make relatively little noise and they are not even heard in the next room. Indeed, noise that cannot be heard in an adjacent room is generally not subject to any avsha milsa concerns even for Ashkenazim. Furthermore, there is no concern that one who does hear the alarm would accuse you of violating Shabbos because setting a clock (or lights or air-conditioning) on a timer is so common. Finally, Ashkenazim can often be lenient with avsha milsa in a case of need, and ensuring that one is awake in time for the morning prayer qualifies as “a case of need.”

  Shabbat 18a; Beitza 27a; OC 252:5; Chazon Ish 38:2–4;