Motion-Sensing Lights and Shabbat Prohibitions

תָּנָא: נֵר שֶׁאֲחוֹרֵי הַדֶּלֶת — פּוֹתֵחַ וְנוֹעֵל כְּדַרְכּוֹ, וְאִם כָּבְתָה — כָּבְתָה. לָיֵיט עֲלַהּ רַב. אֲמַר לֵיהּ רָבִינָא לְרַב אַחָא בְּרֵיהּ דְּרָבָא, וְאָמְרִי לַהּ רַב אַחָא בְּרֵיהּ דְּרָבָא לְרַב אָשֵׁי: מַאי טַעְמָא לָיֵיט עֲלַהּ רַב? אִילֵּימָא מִשּׁוּם דְּרַב סָבַר לַהּ כְּרַבִּי יְהוּדָה, וְתָנָא קָתָנֵי לַהּ כְּרַבִּי שִׁמְעוֹן. מִשּׁוּם דְּרַב סָבַר לַהּ כְּרַבִּי יְהוּדָה, כׇּל דְּתָנֵי כְּרַבִּי שִׁמְעוֹן מֵילָט לָיֵיט לֵיהּ?! אֲמַר לֵיהּ: בְּהָא אֲפִילּוּ רַבִּי שִׁמְעוֹן מוֹדֶה. דְּהָא אַבָּיֵי וְרָבָא דְּאָמְרִי תַּרְוַיְיהוּ: מוֹדֶה רַבִּי שִׁמְעוֹן בִּ״פְסִיק רֵישֵׁיהּ וְלָא יְמוּת״. אָמַר רַב יְהוּדָה: פּוֹתֵחַ אָדָם דֶּלֶת כְּנֶגֶד מְדוּרָה בְּשַׁבָּת. לָיֵיט עֲלַהּ אַבָּיֵי. בְּמַאי עָסְקִינַן? אִילֵימָא בְּרוּחַ מְצוּיָה — מַאי טַעְמֵיהּ דְמַאן דְּאָסַר?! אִי בְּרוּחַ שֶׁאֵינָהּ מְצוּיָה — מַאי טַעְמָא דְמַאן דְּשָׁרֵי?! לְעוֹלָם בְּרוּחַ מְצוּיָה: מָר סָבַר גָּזְרִינַן, וּמָר סָבַר לָא גָּזְרִינַן.

It was taught: With regard to a candle behind a door, one may open and shut the door in his usual manner, and if it is extinguished, it is extinguished. Rav would curse one who did so. Ravina said to Rav Aḥa, son of Rava, and some say that Rav Aḥa, son of Rava, said to Rav Ashi: What is the reason that Rav cursed and reprimanded one who did so? If you say it is because Rav holds in accordance with the opinion of Rabbi Yehuda that it is prohibited to perform an unintentional act from which a prohibited labor could ensue, and the tanna taught in accordance with the opinion of Rabbi Shimon that it is permitted to perform an unintentional act in those circumstances; because Rav holds in accordance with the opinion of Rabbi Yehuda, he curses anyone who teaches the halakha in accordance with the opinion of Rabbi Shimon? They rely on the ruling of a tanna, whose opinion is legitimate. He said to him: In this case, even Rabbi Shimon concedes that it is prohibited, as it was Abaye and Rava who both said that Rabbi Shimon concedes in a case of: Cut off its head, will it not die? In an instance where the unintentional act leads to an inevitable prohibited consequence, even Rabbi Shimon agrees that the person who performs the unintentional act is liable. Rav Yehuda said: A person opens a door opposite a fire on Shabbat. The Gemara relates that Abaye would curse anyone who did so. The Gemara clarifies: With what are we dealing? If you say this is referring to a case where a typical wind is blowing outside, what is the reason of the one who prohibits opening the door? A typical wind will neither fan nor extinguish the fire. And if it is referring to a case where an atypical wind is blowing outside, what is the reason of the one who permits opening the door? The Gemara answers: Actually, it is referring to the case of a typical wind. However, one Sage, Abaye, holds that we issue a decree prohibiting to open the door in the case of a typical wind due to a case of an atypical wind, and the other Sage, Rav Yehuda, holds that we do not issue that decree.

הַמַּבְעִיר כָּל שֶׁהוּא חַיָּב. וְהוּא שֶׁיְּהֵא צָרִיךְ לָאֵפֶר. אֲבָל אִם הִבְעִיר דֶּרֶךְ הַשְׁחָתָה פָּטוּר מִפְּנֵי שֶׁהוּא מְקַלְקֵל. וְהַמַּבְעִיר גְּדִישׁוֹ שֶׁל חֲבֵרוֹ אוֹ הַשּׂוֹרֵף דִּירָתוֹ חַיָּב אַף עַל פִּי שֶׁהוּא מַשְׁחִית. מִפְּנֵי שֶׁכַּוָּנָתוֹ לְהִנָּקֵם מִשּׂוֹנְאוֹ וַהֲרֵי נִתְקָרְרָה דַּעְתּוֹ וְשָׁכְכָה חֲמָתוֹ וְנַעֲשָׂה כְּקוֹרֵעַ עַל מֵתוֹ אוֹ בַּחֲמָתוֹ שֶׁהוּא חַיָּב וּבְחוֹבֵל בַּחֲבֵרוֹ בִּשְׁעַת מְרִיבָה שֶׁכָּל אֵלּוּ מְתַקְּנִים הֵן אֵצֶל יִצְרָן הָרַע. וְכֵן הַמַּדְלִיק אֶת הַנֵּר אוֹ אֶת הָעֵצִים בֵּין לְהִתְחַמֵּם בֵּין לְהָאִיר הֲרֵי זֶה חַיָּב. הַמְחַמֵּם אֶת הַבַּרְזֶל כְּדֵי לְצָרְפוֹ בְּמַיִם הֲרֵי זֶה תּוֹלֶדֶת מַבְעִיר וְחַיָּב:

A person who kindles even the smallest fire is liable, provided he needs the ash that it creates. However, should a person kindle a fire with a destructive intent, he is not liable, for he is causing ruin. Nevertheless, a person who sets fire to a heap of produce or a dwelling belonging to a colleague is liable, because his intent is to take revenge on his enemies. [Through this act,] he calms his feelings and vents his rage. He is comparable to a person who rends his garments over a deceased person or in rage [on the Sabbath], or a person who injures a colleague in an argument. These individuals are all considered to be performing a constructive activity, because of their evil inclinations. Similarly, a person who lights a candle or wood, whether to generate warmth or light, is liable. A person who heats iron in order to strengthen it by submerging it in water is liable for [performing] a derivative [of the forbidden labor] of kindling.

כבר נתבאר בריש סימן הקודם, שמותר להתחיל במלאכה בערב שבת אף שהמלאכה נגמר בשבת. ולכן יכול אדם להעמיד קדירה עם תבשיל על האש בערב שבת סמוך לחשיכה, או בשר בתנור או על גבי גחלים, והן מתבשלין והולכין בשבת. אמנם יש בדברים אלו מה שאסרו חכמים לעשות כן, משום גזירה שמא יחתה בגחלים בשבת כדי למהר בישולם, משום דהחיתוי הוא ברגע אחת, והוא בתאוותו להאכילה - קרוב הדבר שעל רגע זו ישכח ששבת היום, ויחתה בגחלים ויבא לידי איסור דאורייתא, מפני שעל ידי חיתויו תתמהר לבשל, והוה מבשל בשבת. לפיכך עשו חכמים גדרים לזה, כמו שיתבאר בס"ד.

Motion Detectors Another mode of surveillance involves use of a motion detector that causes lights to turn on when the movement of a person is detected. In isolated areas the resultant illumination prevents intruders from breaking and entering under cover of darkness and at the same time serves to provide a measure of physical safety for persons who would otherwise be entering the house or passing down the street in the dark. Rabbi Padwa permits ordinary activity in the presence of such devices in reliance upon two separate considerations: 1) the permissive view of the Arukh with regard to a pesik reisha de-lo niḥa leih; 2) the view of Rashba, cited by Magen Avraham, Oraḥ Hayyim 316:11, permitting a person to close the door of a room in which a deer has sought refuge on Shabbat even though as a result of closing the door, the deer will be "captured." Although neither of those positions is accepted by the codifiers of Halakhah, Rabbi Padwa nevertheless asserts that, taken in combination, they may be relied upon.