The poskim disagree about the status of a watch. Some maintain that only if it is decorative like jewelry may it be worn in the public domain. The test for whether it can be considered decorative is what the owner does if the watch stops. If he would take it off, it indicates that the watch is not jewelry and is used only to tell time. Since that use is not for the sake of his body, wearing the watch in the public domain is considered carrying and is prohibited on Shabbat. In contrast, if the owner leaves it on even when it has stopped because it is decorative (for example, if it is made of gold), then it is deemed jewelry and may be worn in the public domain.
Many poskim maintain that since a watch is worn on the body as is clothing – a person without a watch feels as if he is not fully dressed, and the normal use of a watch is while it is on the body – it follows that the watch is secondary to the body. Thus it is considered like an item of clothing or jewelry, which may be worn on Shabbat in a reshut ha-rabim. The primary opinion is the lenient one, but one who chooses to be stringent should be commended.
A serious problem arises for people who live in or visit an area without an eruv. What can they do when they leave the house and need to take a key with them? The solution is to use the key as a belt buckle. This means one should take a shoelace and thread it through the key, tie it with a bow knot, and put it on as a belt, so that the key will serve as a buckle. In this way one may wear the key in the public domain (SSK 18:49-50; see n. 10 above).
There are places where people must carry an identity card or passport on their person at all times. If someone there must go out on Shabbat for a great need or for the sake of a mitzva, he should carry the passport or identity card with a shinui. For example, he may place it under his hat, or inside his shirt where it is held up by his belt. In this way, one does Hotza’ah via a shvut di-shvut, which he may do for a great need or for the sake of a mitzva (above 9:11).
Similarly, if a doctor has ordered a patient not to leave the house without carrying a certain medication, the patient may go out for a great need or for the sake of a mitzva, as long as he carries the medicine with a shinui. One who must rely on this leniency should try not to come to a stop in the reshut ha-rabim until he reaches the reshut ha-yaĥid that is his final destination (SSK 40:7; n. 3 above).
In a place without an eruv, if life-and-death security concerns demand that people carry a gun and a cell phone, these items may be taken along on normal Shabbat activities. The phone should be carried with a shinui, but the gun should be carried normally, as carrying it with a shinui could be dangerous. One may not go out on Shabbat with a gun or a walkie-talkie just for an outing. This rule will be explained in detail later on (27:17).
. SSK 18:27 follows the first opinion but adds that those who are lenient have grounds for their leniency. Yaskil Avdi 7:19 and Le-horot Natan 4:26 state similarly. It seems that Minĥat Yitzĥak 1:67 is stringent even when a watch is made of gold. In contrast, R. Shlomo Zalman Auerbach is lenient, as cited in SSK ch. 18 n. 113. Similarly, Igrot Moshe states that the primary ruling permits wearing a watch (OĤ 1:111). This is also the opinion of Yeĥaveh Da’at 3:23 and Menuĥat Ahava 3:27:33. In an area enclosed by an eruv, even those who are normally stringent and do not rely on an eruv of the tzurat ha-petaĥ type for streets wider than sixteen amot are lenient to allow wearing a watch there.
. First, everyone agrees that the shinui renders the prohibition rabbinic in this case. Second, for those who maintain that there is no reshut ha-rabim today, this becomes a shvut di-shvut. Third, Maharash Engel 3:43 explains that this act of carrying is a melakha she-eina tzerikha le-gufah, because the person does not need the identity card for its own sake (le-gufah), but only to protect himself. However, it is difficult to claim that one who must carry medication does not need the medicine for its own sake (see Tzitz Eliezer 13:34). According to those who maintain that there are areas that qualify as reshut ha-rabim even nowadays, there is less room for leniency. Thus, it is proper when carrying medication to avoid stopping in reshut ha-rabim, as explained above in n. 3 (see Nishmat Avraham 301:2, n. 1). Le-khatĥila, one should not stop when carrying an identity card either.