The Shulhan Aruch (Hoshen Mishpat 291:1) codifies the basic laws regarding a Shomer Hinam – somebody who agreed to watch over another person’s possession without pay (listen to audio recording for precise citation). Halacha exempts such a guardian from liability for the loss of or damage to the possession, except in the case of "Peshi’a," or gross negligence. He is not required to compensate the owner for the loss or damage unless he was negligent and did not watch over the item with basic standards of diligence.
The Shulhan Aruch mentions that although a Shomer Hinam is generally exempt from liability, he is required to make an oath that he acted responsibly and was not negligent, if the item’s owner demands such an oath. In principle, the guardian must make this oath in Bet Din (the Rabbinical Court) while holding a Torah scroll. However, nowadays we do not allow taking oaths in this fashion, given the gravity of the sin of uttering a false oath while holding a Torah scroll. Therefore, when such a case comes before Bet Din, the court will work with the litigants to reach a mutually acceptable settlement, or convince the owner to accept the guardian’s claim without an oath.
A common example of this kind of situation is a person who asks somebody to watch his briefcase for him at the bus stop, such as if he needs to run into a store for ten minutes. If the briefcase is missing when he returns to the bus stop, must the guardian pay him the value of the briefcase’s contents? If he returned after ten minutes, beyond the period for which the guardian agreed to watch the briefcase, then the guardian certainly bears no liability, since he never accepted responsibility beyond the stipulated time-frame. However, if the owner returned within the designated time period, then the guardian’s liability will depend on the circumstances under which the briefcase was lost. If he was grossly negligent, and placed the briefcase in a place where he could not see it, then he certainly bears liability and must compensate the owner. If, however, he was watching the briefcase, but the thief employed some sly tactic to grab it, then the guardian does not bear liability. Since he watched the briefcase at an acceptable standard of diligence, he has fulfilled his duty and does not bear any liability.
(A separate question arises as to how we determine the value of the briefcase’s contents if, indeed, the guardian acted negligently and thus bears liability. The owner may claim, for example, that the briefcase contained a large amount of cash. The issue of determining the value of the contents is an important and complex one, and deserves independent treatment in a separate context.)
Summary: One who agrees to watch another person’s possession without pay does not bear liability if the item is lost, unless he was negligent and did not watch the item with basic diligence. In principle, he must make an oath that he was not negligent, but since oaths are discouraged nowadays, the court in such a case will help the parties reach a reasonable settlement, or persuade the owner to accept the guardian’s claim without an oath.
