Pesik Raishai - An Inevitable Result

- A neighbor has installed a photo-optical device in his yard. When you innocently pass by on the sidewalk, a security light goes on. Does this mean that you cannot walk on the street on Shabbat?
- All the members of the household are seated at the Shabbat meal. The room is hot and stifling. Is one permitted to open a window? Isn't there a danger that an incoming breeze will have an effect on the candles?
Such questions are very common. Is labor prohibited on Shabbat even it is unintentional and incidental? The sages ruled that "something that is unintended" is not prohibited on Shabbat, but they make a condition that the consequence should not be an unavoidable result of the action. The usual example, in the words of the sage, is: "Pesik raishai velo yamut? - If you chop off its head, won't it die?" That is, one who cuts off the head of a bird as a game cannot claim that he did not intend for the bird to die. This is an unavoidable consequence of his action.
But this general approach has also been restricted by the early commentators. Even if the result is definite, the labor will not be considered as intentional if the person is "uncomfortable" with the outcome and is not at all interested in it. In practice, most of the early commentators do not allow "an unwanted unavoidable result" on Shabbat as a general rule, but under special circumstances and with the addition of certain halachic conditions it is possible to be lenient and allow the action.
Many problems of the type discussed above are encountered as a result of the progress of modern technology. Many electrical instruments contain various types of detectors. Examples are light sensors (photo-electric), heat detectors (thermostats), level sensors (floats, pressure sensitive devices), close approach (magnetic detectors), and others. These react to the presence or activity of a person, either with or without his knowledge. When is such action considered something that a person desires? Every case must be analyzed individually. Special attention is required with respect to especially "sensitive" equipment, such as refrigerators, hot water urns, water purification systems, systems for maintaining a high pressure, etc.

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