Any of the laws of Shabbat are set aside in the case of a life-threatening emergency. Indeed, it is a mitzvah to violate the Shabbat to save a life, and is, in fact, not considered a violation of the Shabbat. This applies even if there is only the slightest doubt that a life is in jeopardy.

For example, if a person falls ill and there is even the slightest chance that his or her condition is life threatening, we call a doctor, drive to the hospital, and so on. Another example is in the case of war or threat of attack, all necessary defense measures are taken. In the words of the Talmud, "it is better to violate one Shabbat on the person's account, so that he should keep many more Shabbatot."