==Setting Timers before Shabbat==
# It is permitted before [[Shabbat]] to set a timer for lights or other electric appliances to go on or off on [[Shabbat]].<ref>Sh"t Maharam Shik 157, Chazon Ish 38:2, Shemirat [[Shabbat]] KeHilchata 13:26, Menuchat Ahava 24:30, Sh"t Yabia Omer 3:17.
* Ben Yehuda (responsa 151) writes that it is rabbinically forbidden to use a timer that turns on a light on Shabbat. He writes that there's no Biblical melacha to set a timer since it was all put in place before Shabbat as per the Nemukei Yosef b"k 10a. However, he writes that it is rabbinically forbidden based on the opinion of Rabba in Shabbat 18a who says that it is a disgrace to Shabbat to leave grain in a water-grinder that will become ground on Shabbat. Rav Yosef in the gemara argues that it is permitted and only forbidden according to Bet Shamai. The Shulchan Aruch 252:5 rules like Rav Yosef but the Rama is stringent unless it will result in a loss. He says that based on the Rama it is forbidden to set a timer before Shabbat and even though everyone knows that it is set before Shabbat that logic isn't applicable if the melacha in question is Biblically forbidden. The Kaf Hachaim 252:
72 cites this opinion.</ref>
# One may set an alarm clock before [[Shabbat]] even though it will make noise on [[Shabbat]]. <ref>The [[Shabbos]] Home (Rabbi Simcha Cohen, vol 2, pg 537) and Sh"t Maharshag YD 1:7(2) permit. However, Sh"t Igrot Moshe 4:70(4) only permits if it is not heard outside his personal room. See Shemirat [[Shabbat]] KeHilchata 28:29 (and 28:30 in new edition) who permits before [[Shabbat]] for mitzvah purposes setting a mechanical alarm clock that involves removing a pin (see there). </ref> See [[Making music on Shabbat]].
# Some forbid leaving a digital photo frame which presents a slideshow of pictures set from before [[Shabbat]] to continue during [[Shabbat]]. <ref>[http://www.ou.org/webcast_kosher Rav Hershel Schachter] (OU Kosher Webcast, 2011, min 16-8) </ref>