Would one be allowed to use an air purifier with an LED smell indicator sensor on Shabbat if bringing in odors near the purifier with outside food or other odorous things could or most surely would trigger an LED sensor to go off? The resulting activation of the LED lights would be undesired and the trigger would technically be an indirect delayed activation unlike walking directly in front of a motion LED sensor. The benefit of the purifier would be to control allergy symptoms whereas without it allergies would be worse. Also there is no way to disable the LED lights.

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    How is this different from a thermostat? Doing any activity affects the ambient temperature in some way.
    – Double AA
    May 18, 2017 at 14:55
  • Other than the question of the LED light (which may be a "grama" issue), there may be a question of using this ant-allergy purifier for medicinal purposes on Shabbat.
    – DanF
    May 18, 2017 at 14:56
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    @DanF I'm uncertain if the gezeirah against medicines can be applied to non-consumable items that are generically beneficial - people like to breathe clean air. The only items prohibited in the gemara (IIRC) are as cures to specific maladies, not general well being. May 18, 2017 at 15:02
  • @IsaacKotlicky You may be right. I know that we have had discussions on the Shabbat medicine area, previously (I think the "Netti pot"?? This may be similar to that area. I have to review that discussion. It's been a while, and I think it's unresolved.
    – DanF
    May 18, 2017 at 15:08
  • Assuming you know for a fact that your actions will cause the light to go on, then this is an example of a psik reisha sh'lo nicha lei. (Admittedly on a d'rabbanan since it's an LED light). That topic is subject to a machloket, so the answer is "call your local rabbi". May 18, 2017 at 19:27

1 Answer 1


Rav Nachum Rabinovitch, shlit"a, (who holds electricity is only, at worst, an issue of uvda d'chol [weekday activity] has ruled allowing the use of hotel key cards even when they trigger an LED (see here). Your scenario would seem to be even less of an issue. (I believe he has also accordingly allowed the use of baby monitors even where an LED indicates crying.)

Similarly, according to those such as the Chazon Ish, z"l, who hold that electricity would only be an issue of causing a useless item to become a useful tool (mekeh b'patish-finishing a utensil) or structure (boneh-building), this scenario would seem to be fine since the device is operational before the LED is triggered.

The only issue might be according to those, such as Rav Chaim Ozer, z"l, who hold that electricity is a corollary of lighting/extinguishing a fire. Notably, while an incandescent bulb, which generates both heat and light, is arguably included within the Talmudic example of a gacheleth shel matecheth (burning metal shard; see here and here), an LED does not generally involve significant heat, which perhaps suggests it should not be classes as esh. (This argument might require assuming that the amud esh [pillar of fire] in the desert did generate heat - which may be a reasonable interpretation regardless considering the desert does typically get cold at night.) In any case, I am under the impression that Rav Shlomo Zalman Auerbach, z"l, who originally held like Rav Chaim Ozer, z"l, retracted after in-depth consultations with scientific experts in the field, though he was unwilling to reverse the popular stringent view of electricity in general.

  • I am not clear on your take on Rav Shlomo Zalman Aurbach's postion regarding electricity,in his Minchas Shlomo he goes in depth explaining that the prohibiton of electricity is only a minhag ,and in reality should be mutar ,he does give heterim in special cases...is that what you meant?
    – sam
    May 22, 2017 at 1:49
  • @sam Perhaps. I haven't read it inside. Though I have trouble believing he held it should be binding as a minhag if his understanding was that the minhag itself was created based on a mistaken understanding of the phenomenon.
    – Loewian
    May 22, 2017 at 1:59
  • its worth while to read it,he goes through all postions and explains how they are incorrect and comes to the conlcusion to assur it based off minhag Yisrael,very intresting take ,a postion which is very hard to beileve unless read from the actual source
    – sam
    May 22, 2017 at 2:03

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