One of the wonders of modern technology is voice activation, the ability to activate certain devices with one’s voice. We can now "consult" with devices to access information (such as Siri and Alexa), and there are systems which allow people to control lighting, air conditioning and other functions through their voice.
How does Halacha view performing a Melacha (activity forbidden on Shabbat) in this fashion? Is activating a light with one’s voice akin to turning it on manually? And even if not, would this fall under the same prohibition as "Amira Le’akum," which forbids asking a gentile to perform Melacha on one’s behalf on Shabbat?
Of course, this subject is not explicitly addressed in our Halachic sources, but our tradition is timeless and relevant in any age, and thus we indeed find a number of sources that speak about performing Melacha with one’s voice, and which thus may shed light on our question.
One such source is a discussion concerning the practice to recite Sidkatecha on Shabbat afternoon during Minha. The Rosh (Rabbenu Asher Ben Yehiel, Germany-Spain, 1250-1327) writes that the custom was also to spend some time in silent contemplation, as Shabbat afternoon was the time when Moshe Rabbenu died. We recite "Sidkatecha," a pronouncement of Siduk Ha’din (affirming G-d’s justice), and spend some time in somber contemplation, to mark the death of Moshe Rabbenu. However, the Rosh raises the question of how it is possible that Moshe died on Shabbat, given the Midrash’s comment that Moshe wrote thirteen Torah scrolls on the day he died. (He gave one scroll to each tribe, and the thirteenth was kept in the Mishkan.) Writing, of course, is forbidden on Shabbat, and so it is difficult to understand the tradition that Moshe died on Shabbat. To answer this question, the Hatam Sofer (Rav Moshe Sofer of Pressburg, 1762-1839) writes in one of his responsa (vol. 6) that Moshe must have written these Sifreh Torah not by hand, but rather by pronouncing different Names of G-d. After all, it does not seem physically possible for one person to write thirteen complete Sifreh Torah in a single day. Necessarily, then, Moshe did not actually write the scrolls, but rather had them written with his voice, by pronouncing G-d’s Names. Therefore, the Hatam Sofer writes, this was permissible on Shabbat, because writing in this fashion is not included under the Torah prohibition writing.
At first glance, this responsum of the Hatam Sofer indicates that a Melacha performed by voice, as opposed to action, is not forbidden on Shabbat.
However, a number of Poskim draw a fundamental distinction between Melachot performed through supernatural means, and Melachot performed through advanced technology. Moshe’s "writing" Sifreh Torah by pronouncing the Names occurred outside the laws of nature, and it is for this reason that it was allowed on Shabbat. But if one performs a Melacha by voice within the laws of nature, such as when using modern-day voice activation systems, this would be included in the Shabbat prohibitions, and would thus be forbidden.
We find other sources, too, which speak of a Melacha performed by voice through supernatural means. The Shulhan Aruch (Orah Haim 328) rules that trapping a snake "Al Yedeh Lahash" – by reciting an incantation – is permissible on Shabbat. (Normally, trapping a snake is forbidden on Shabbat unless it attacks a person.) The Mishna Berura (Rav Yisrael Meir Kagan of Radin, 1839-1933) explains that this is allowed because the trapping is done in a manner "Le’ma’ala Min Ha’teba" – outside the laws of nature. Hence, this ruling does not shed light on our question, which involves a Melacha performed with one’s voice without utilizing supernatural forces.
Similarly, Rav Haim Palachi (Turkey, 1788-1868), in his Leb Haim, permits on Shabbat reciting certain verses which have the power to extinguish a fire. Since this is a supernatural form of extinguishing, he writes, this does not fall under the prohibition of extinguishing on Shabbat. This ruling, too, has no bearing on our question, which regards the case of a Melacha performed through speech without enlisting supernatural forces.
One might draw proof to the contrary, that a Melacha performed by speech is forbidden on Shabbat, from the Shulhan Aruch’s ruling (Hoshen Mishpat 420) that one who causes physical harm to a person by shouting in his ear is liable for the damages. This ruling clearly indicates that as far as the laws of Nezikin (torts) are concerned, the effects of one’s voice are no different from the effects of one’s physical actions. The question then becomes whether we may apply this principle also to Shabbat. Do Shabbat and Nezikin share the same definitions of a physical act for which one is held accountable? Or does the definition of an "act" with respect to Nezikin have no relevance to the laws of Shabbat?
The answer to this question might be found in the Talmud Yerushalmi (Shabbat), which addresses the case of a person who blows on two candles, causing one flame to be extinguished, and the other – which was flickering – to be steadier. Interestingly, the Yerushalmi comments that the person has committed two Shabbat violations – he extinguished one candle, and he caused the other candle to shine more brightly, which is akin to kindling. The Yerushalmi then proceeds to note the significance of the fact that expanding a flame by blowing is Halachically equivalent to kindling. On this basis, the Yerushalmi comments, we may conclude that if somebody blows fire onto somebody’s property, he is liable for damages caused by the fire, even though he caused the damage through blowing, and not by kindling a fire. Seemingly, this shows that Halacha indeed compares Shabbat and Nezikin in this regard, such that we might assume that just as one is liable for damages causing by shouting into a person’s ear, he is similarly liable for a Melacha performed by speaking to a device.
Some have argued that when one performs a Melacha with his voice, this constitutes a "Shinui" – a deviation from the normal way of performing the Melacha. However, even if this were true, it would still be forbidden, as performing a Melacha in an unusual manner is forbidden on the level of Rabbinic enactment. Secondly, it seems very difficult to consider talking to such a device a "Shinui," given that this is precisely the way the device is meant to be used. (This is similar to kicking a soccer ball, which violates the prohibition of Mukseh, even though normally, the prohibition of Mukseh forbids only handling Mukseh objects with one’s hand. Since the usual manner of handling a soccer ball is by kicking it, this is forbidden on Shabbat.)
The same is true of the suggestion that performing a Melacha through voice activation constitutes Gerama – an indirect Melacha. Gerama on Shabbat is prohibited on the level of Rabbinic enactment, and even if not, this would hardly seem to qualify as Gerama, given that there is no delay, and the result occurs immediately as a result of one’s voice.
One might, however, nevertheless conclude that performing a Melacha in this fashion is forbidden only on the level of Rabbinic enactment, but for a different reason. The thirty-nine categories of forbidden activity on Shabbat are based upon the activities which were performed in the construction of the Mishkan in the desert. The Poskim debate the question of whether the Torah prohibitions are limited to activities which resemble the corresponding actions which were performed in the construction of the Mishkan. The Hatam Sofer ruled that opening an umbrella would not fall under the prohibition of making an Ohel (tent) on Shabbat, because the Mishkan was a stationary Ohel, and an umbrella, of course, is a tent which one carries with him. The Noda Bi’yehuda (Rav Yehezkel Landau of Prague, 1713-1793), by contrast, disagreed, and ruled that although an umbrella differs substantially from the Mishkan, it nevertheless falls under the Torah prohibition of making an Ohel on Shabbat. This appears to be the commonly accepted view – that activities are forbidden on Shabbat if they produce the result of one of the thirty-nine Melachot, even if they substantially differ from the way the corresponding Melacha was performed in the Mishkan. If so, then, seemingly, performing a Melacha through voice activation would constitute a Torah violation.
Some also suggest that activating a device through voice might fall under the prohibition of "Ve’daber Dabar," which forbids speaking about weekday matters on Shabbat. However, one could easily circumvent this issue by programming the device in question to respond to a word which has no weekday association.
In any event, based on all we have seen, it is clear that performing a Melacha through voice activation is forbidden, and might likely be forbidden on the level of Torah prohibition.
In conclusion, it is worth noting how this entire discussion demonstrates the eternal relevance and applicability of the Torah. Our ancient Torah tradition can and must be applied even to cutting-edge technology, and guide us even with regard to inventions and technologies which our ancestors could never have imagined, because Torah is eternal, eternally relevant, and eternally binding.
Summary: It is clear that activating systems through voice – such as posing questions to Siri or Alexa, or speaking to activate lighting, air conditioning and the like – is forbidden on Shabbat. While it might possibly be forbidden only Mi’de’rabbanan – on the level of Rabbinic enactment – it is certainly forbidden, and may likely be forbidden on the level of Torah prohibition.