Obviously they wouldn't need a "blech" like we think of one, but would they need some sort of physical alteration to remind one not to adjust the knobs/switches on Shabbos?

More specifically, to leave a light or fan on on Shabbos, would one have to place a cover or piece of tape over the knobs and switches as a reminder? And if not, why not?

  • Depends on how likely you are to flip switches if you don't put this on. My wife & I still tape some light switches that we know are likely to be flipped if not taped.
    – Ze'ev
    Commented Sep 10, 2012 at 18:36

2 Answers 2


The issue applies only where the chachamim were specifically concened. One area of concern is performing acts which require seeing something well, like reading (Shulcha Aruch O.C. 275), where the chachamim were concerned we may inadvertently add oil to the wick to burn it brighter. There is a machlokes brought in the Mishna Berurah whether a heker works.

We are lenient in this law, certainly when using non-adjustable lights, since there is no gezeirah that one will come to light a lamp (probably because that takes more time and one will remember he may not do so).

As far as adjustable lights (dimmers) I don't know.

Fans do not fit into the reasoning, nor was there any such gezeirah.


Yes. technically you would need to cover knobs and switches not as a reminder, but to prevent yourself from turning switches on and off...

check the shoulchan arouch shin yud chet.

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