A Shabbat alarm clock

Hi,

One may not set an alarm clock to wake him up on Shabbat morning if the sound will be heard beyond his room, and certainly his house. People normally set their alarms on the previous night, and so those who hear the sound will assume he set the alarm on Shabbat.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:70:6)

[Yes, this does raise questions in related cases, such as an afternoon alarm, or an alarm which will be heard outside one's room but only by those who know it was set before Shabbat.]

Have a great day,
Mordechai