Mrs. Melamed is a high-school teacher. One afternoon at 3:45 she saw her colleague, Mrs. Klass, rushing out of the building.

“We’re hosting a sheva brachos tonight for my niece,” Mrs. Klass said. “I don’t even have a minute to return my projector to the office. Would you mind keeping it overnight in your office?”

“With pleasure,” replied Mrs. Melamed. She took the projector to her office, where she had a free hour until 5:00.

Mrs. Melamed was grading a paper when she suddenly noticed that it was 5:01. She gathered her books and ran to her classroom. In her haste, she forgot to lock her office.

After teaching a double-period, Mrs. Melamed returned to her office. The desk where she had left Mrs. Klass’s projector was empty!”

“I can’t believe it!” Mrs. Melamed cried out.

Mrs. Melamed immediately called her husband. “Mrs. Klass gave me her projector to keep overnight in my office,” she said. “I ran out to teach and left it unlocked. Someone came into the room and stole the projector!”

“This sometimes happens,” her husband soothed her. “I’m not sure you’re liable if people don’t always lock their offices.”

Mrs. Melamed called Mrs. Klass. “I don’t know what to say,” she began. “I ran out to teach and left my office unlocked. While I was teaching, someone came into my office and stole your projector.”

“That was an expensive projector,” said Mrs. Klass. “It cost me $900. You were negligent in leaving the office unlocked.”

“But I often leave my office unlocked,” said Mrs. Melamed. “I’ve left a projector in my office unlocked and never had a theft before. Why should I have to treat your projector better than my own?”

“The fact that you risk leaving your office unlocked doesn’t mean that it’s acceptable,” said Mrs. Klass. “Almost everyone locks their office; you were negligent.”

“You also once forgot to lock your office overnight!” argued Mrs. Melamed.

“The fact that I am sometimes careless does not excuse your negligence,” said Mrs. Klass. “It’s your misfortune that a thief happened to be roaming the building then.”

“What if I had gone down the hall to get a coffee,” asked Mrs. Melamed. “Would you still consider me negligent?”

“Yes,” said Mrs. Klass. “Doors should always be locked!”

“My husband is not sure that I’m liable if people occasionally leave their doors unlocked,” said Mrs. Melamed. “He suggested that we consult Rabbi Dayan.”

“That’s fine with me,” said Mrs. Klass.

They arranged to meet with Rabbi Dayan. “I asked Mrs. Melamed to watch my projector in her office,” said Mrs. Klass. “She forgot to lock the door and the projector was stolen. Is she liable for the projector? What if she had gone down the hall for coffee?”

“If it is customary in your school to lock the office doors, Mrs. Melamed is liable for the projector when she left the office unlocked,” ruled Rabbi Dayan. “A person is required to guard his friend’s property in the customary manner. Even if a person is careless with his own property, he may not be careless with his friend’s” (C.M. 291:14).

“What if Mrs. Klass would frequently leave her office unlocked?” asked Mrs. Melamed. “Can I be expected to watch better than she does?”

“This case is not commonly addressed,” replied Rabbi Dayan. “It seems, though, that a guardian is required to guard according to what is commonly expected. Thus, you cannot exempt yourself by claiming that Mrs. Klass often leaves her own office unlocked.”

“And if it were customary to leave the doors unlocked?” asked Mrs. Klass.

“In that case, a shomer chinam (unpaid guardian) would be exempt,” answered Rabbi Dayan. “He is expected to watch in the normal, customary, manner. Similarly, if you had gone out for a short time to get a cup of coffee, when many people leave the office unlocked, you would be exempt. However, a shomer sachar (paid guardian) is still liable. He is paid to provide extra protection” (C.M. 291:8; 303:10-11).

I ordered a cab and during the trip I noticed a $100 bill on the floor.

Q:  Am I permitted to keep the money for myself or am I required to give it to the driver or perhaps announce that I found the money?

A:  There are a number of issues that must be addressed. It can be assumed that by the time you found the money the person who lost it was aware that it was lost. People regularly check their pockets and the owner would have realized that it was lost, but since money does not have a siman — identifying mark — he despaired of recovering it (C.M. 262:3).

However, perhaps the cab driver acquired the money by virtue of the fact that it was found on his property. A person’s property, even a movable property (C.M. 200:3), is capable of acquiring items that are in or on it, even without the owner’s awareness. (To determine whether a car is considered chatzer mehaleches — literally: a walking domain, which cannot affect a kinyan, see Pischei Choshen Kinyanim 8:[63]).

Seemingly, a precedent for such a conclusion can be traced to the halachah concerning one who finds money in a store (C.M. 260:5). If the money is found in the area where customers walk, the money belongs to the finder. In that case as well, why doesn’t the lost object belong to the storeowner since it was found on his property?

One answer is that since customers walk around in that area, it is not protected, and as a result the storeowner does not rely on the ability of his property to acquire for him lost objects (Shach 260:18). Similarly, one who finds money in a cab may also keep it for himself since it is not protected and thus the driver does not have in mind that he should acquire it for himself.

Another reason the cab driver does not acquire the money is that according to many authorities, if one’s property acquired the money when the owner dropped it, he would be taking another person’s money (issura asa l’yadai), since the owner did not yet despair, not yet having realized that it was missing. In such a circumstance a person’s property does not acquire lost objects on his behalf (Shach 262:1 268:1).

An additional reason the driver does not acquire the lost object is that one’s property does not acquire objects that would not be found. For that reason someone who owns a rental property does not acquire lost objects left behind by previous tenants since it is likely that it will be found by the next tenant rather than by the owner of the property (Ketzos 200:1).

However, if you found an object that has a siman, you would be obligated to make an effort to find the owner. The manner in which that is done is by contacting the cab company and letting them know that if someone calls looking for an object that was left in a cab he should contact you.

Q: Do I have a responsibility to spare my neighbor from loss?

A: If someone faces potential loss, you are obligated to spare him, even if it involves time and physical effort on your part. If hashavas aveidah requires returning items already lost, then all the more so we must protect the owner from suffering loss (C.M. 259:9; Shulchan Aruch Harav, Metzia #31; Pischei Choshen, Aveidah 1:20) Therefore:

If you see thieves breaking into a neighbor’s apartment, you are required to summon the police. Similarly, if you observe a hit-and-run accident, you should provide any details you have.

If water or fire threatens your neighbor’s property, you must alert him. The same applies if he left his water, air conditioner or light on inadvertently.

If a lender forgot about a loan, you should remind him. Similarly, if you can testify on behalf of someone on a monetary issue, you are required to do so (C.M. 28:1).

If someone is about to purchase something from an unscrupulous vendor who overcharges significantly, you should warn him (Chofetz Chaim, Rechilus 9:10-12).

If your friend is ill, you should daven on his behalf (Hashavas Aveidah K’halachah 13:1-6).