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).