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December 15, 2024
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Triggering Outdoor Motion Sensors on Shabbat: Detecting Hashem’s Hand in the Halachic Process

On the way home from Shaarei Orah this past Friday night, I asked my sons to swerve out of range of a motion detector that would trigger a light when we passed by. While my sons happily complied (and even thanked me), one might wonder as to whether this was truly necessary. The answer depends on the resolution of a number of fundamental issues regarding Hilchot Shabbat. Rav Hershel Schachter addressed this issue in a shiur he delivered at TABC in May 2005.

Unintentional Results:

Davar She’eino Mitkaven

Offhand, it would seem that this should be questionably permissible. After all, the dispute that rages between Rabi Shimon and Rabi Yehuda throughout Shas as to whether a davar she’eino mitkaven (an unintended action) is permitted, is resolved in favor of the lenient view of Rabi Shimon.

However, this is not so simple, as even Rabi Shimon would rule strictly in a case of pesik reisha, where it is inevitable that melacha will result. Moreover, the result is desired (as the light makes it easier to walk), making it a pesik reisha d’niha le, which is undoubtedly forbidden.

A Surprising Rashba

Nonetheless, there is a strong reason to be lenient. The Mishna (Shabbat 106b) permits, as explained by the Rashba (Shabbat 107a), closing a door on a house even though one thereby traps a deer inside the house. The Rashba surprisingly explains that since one’s intention when closing the door is to protect the home (and not to trap the deer), no melacha is violated despite the fact that one is aware that the deer is being trapped and that the result is inevitable.

Many Acharonim, including Teshuvot Avne Nezer (Orach Chaim 194), Teshuvot Chelkat Yo’av (1 Orach Chaim 11) and Rav Ovadia Yosef (Teshuvot Yechave Da’at 5:29) explain that since one does not come in direct contact with the deer and does not intend to trap the deer, this renders the action as indirect (gerama). The combination of the fact that it is an unintended act and is gerama renders the act as permissible. Gerama is not forbidden in a case of unintentional causation even in a case of pesik reisha (as explained by the Even HaOzer to Orach Chaim 328).

Rav Schachter explains that this approach fits with the Rambam (Hilchot Nizkei Mammon 4:2 as explained by the Maggid Mishneh ad. loc.) who believes that intention often defines the difference as to whether something is defined as direct or indirect. The Rambam obligates one for damages caused by animals who escape due to his breaking the fence enclosing the animals, only if one’s intention was for the animals to cause damage.

Thus, according to the Rashba, triggering an outdoor sensor light does not violate Shabbat. One’s intention is purely to walk on the street, and although he is aware that he is triggering the sensor to turn on the light, no Shabbat violation occurs. He does not come into direct contact with the light and has no intention to turn on the light and thus one has not transgressed in such circumstances.

The Ran’s Dissent

However, the Ran (Shabbat 38a in the pages of the Rif) strongly rejects the Rashba’s thesis. He believes the conventional rules of davar she’eino mitkaven and pesik reisha apply in such a case. The Ran believes that the case in the Mishna is speaking of where the person closing the door is not aware of a deer being trapped inside the house. Thus it would be forbidden, according to the Ran, to trigger a sensor light since one does benefit from the added light.

Rav Schachter’s Ruling

Rav Hershel Schachter stated that one should try his best to accommodate the Ran’s stricter opinion and avoid triggering the sensor light. However, in case one cannot avoid a sensor light, one may rely on the Rashba’s approach. This ruling may also be followed by Sephardic Jews, as Rav Ovadia Yosef (in the aforementioned Teshuvot Yechave Da’at) adopts the same approach to a similar issue. Thus, the Jachter men acted properly by moving out of the way of the sensor light that they might trigger walking home from Shabbat evening tefilla.

Detecting Hashem’s Hand

In the Halachic Process

Let us reflect a moment on this discussion. A most strange scenario presented in Gemara serves as a precedent to resolve a routine 21st-century scenario. This is hardly an exceptional situation. We find this happening hundreds if not thousands of times in halachic history.

Here are but a few examples: The Gemara (Sanhedrin 77a) speaks of releasing a dam of water and the rush of water killing someone tied up nearby. This serves as a precedent for permitting the opening of a refrigerator on Shabbat despite the fact that this might turn the motor on earlier than expected. Makkot 21a speaks of shaving with a scissors, which serves as a precedent for the discussion of electric razors. Gittin 8b speaks of carrying a Kohen in a box above an impure location, which serves as the basis of the debate about a Kohen riding on an airplane that flies above a cemetery. Gittin 66a speaks of a man trapped in a pit ordering the writing of a Get and this is a possible source that might permit a husband appointing an agent to execute a get via videoconferencing. Chullin 70a speaks of transferring a fetus from one animal to another, which serves as the beginning of the discussion of the status of a baby born to a woman who received the egg from a donor.

A simple perusal of contemporary halachic literature reveals many, many similar examples. What are we to make of this phenomenon? I see this as an expression of Hashem’s hand in the halachic process. How else is it that no matter the advance, poskim invariably find a precedent in the Gemara? What drove the Chazal to include such bizarre discussions that time after time emerge as crucial precedents for issues of major importance in the age of rapid technological development? I, for one, see no reasonable explanation other than the subtle hand of Hashem quietly guiding the sages of the Talmud to provide the raw material that enables the eternal Torah to retain its relevance and vitality in all circumstances and all generations.

Note: We expect to print a lengthier version of this piece in TABC’s Kol Torah.


Rabbi Haim Jachter is the spiritual leader of Congregation Shaarei Orah, the Sephardic Congregation of Teaneck. He also serves as a rebbe at Torah Academy of Bergen County and a dayan on the Beth Din of Elizabeth.

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