[Avodah] electronics on shabbat

[Akiva Miller via Avodah]

R' Eli Turkel posted:

> A psak of R Rabinowitz allows the use of card readers and
> many other gadgets used for opening hotels doors on shabbat
> see for more details
<http://www.aishdas.org/avodah/faxes/rnerElectronicsShabbat.pdf>

Here's the excerpt that I want to focus on:

> However, according to HaRav Rabinowitz, today, many electronic
> devices do not result in the closure of a circuit or creation
> of a new flow of electricity and the circuits are based on
> miniature automatic semi-conductors, in which the current is
> virtually undetectable and therefore uvda d'chol is not applicable.

What does "virtually undetectable" mean? In context, he seems to take it to
mean the same thing as "UNdetectable", but I would think it is the same as
"IS detectable". What is the shiur of detectability?

Even if he has proven that there's no melacha here, how does that prove
that uvda d'chol is not applicable? The whole idea of invoking uvda d'chol
is for situations where there's no melacha. You have to ask whether the
activity is Shabbosdik, and if it isn't, then it is an uvda d'chol, whether
there's  melacha involved or not. (I am not getting into the technical
definition of uvda d'chol here, only isolating it from the concept of
melacha.)

But actually, I am less worried about the "l'halacha", and much more
concerned about the "l'maaseh". How is the average person going to know
whether or not a given device meets these conditions? He himself write that
this applies to "many" such devices. How can I know which ones are
sufficiently advanced?

Another quote:

> In some of the sensors there is an LED indicator but the
> technology of LED is such that there is no ignition/kindling.
> There is no prohibition of "nolad" in this technology according
> to Rabbi Dror Fixler.

Okay, so there's no nolad. What of the much more serious melacha of mav'ir?
Is this not a fire? My understanding is that halachic fire is defined by
either heat OR light. Is Rabbi Fixler requiring heat alone? Is he saying
that because there is no heat from an LED it does not constitute fire,
despite the fact that it does generate light? If that's his view, I would
like to hear more about it.

Akiva Miller
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