Nonetheless, I was wary of him, having had personal experience with security breaches. When I was much younger and living in a brownstone in Manhattan's West 80s, I was standing in my vestibule getting the mail after a long day at work. A stranger came up the steps with a piece of paper in his hand, apparently a messenger.

"Do you know if this person lives here?" he asked me.

I examined the scrap but didn't recognize the name, so I turned away from him to look at the mailboxes. "Did you check...?" I started to ask.

My words were cut off as I felt the man's hands around my throat. "Give me your money," he said.

Without thinking — if I had thought, I would probably have surrendered my wallet — I rammed him back into the wall of the narrow space; he released me and a furious fight ensued, after which my attacker fled.

I thought of this as the strange young man followed my girlfriend up the steps of our six-story walk-up in Manhattan's Morningside Heights neighborhood; I came up behind him with the intention of seeing if he actually was a partygoer. But when we reached our landing, the man stopped, indicating our apartment. "I have to get behind that door, for ten minutes," he said mysteriously.

"You don't live here, do you?" I asked him. He was unsteady on his feet, apparently drunk or high. He shook his head. "You'll have to leave then," I said as matter-of-factly as I could. I escorted him down the stairs. He went quietly — until we got downstairs, when he ran into the street and was nearly hit by a cab.

I don't know what happened to our young visitor — I called the police to report him as a danger to himself — but I do know that security is a big issue in most non-doorman co-ops. When I first moved to my Upper West Side apartment 20 odd years ago, the word on the street was that the street was something to worry about. The man in the hardware store next door to us did a booming business in accordion gates — the kind that slide open and shut, keeping the would-be burglar (and most of the available light) out. One of my neighbors, who lived on the top floor and had been burglarized in his last home in Boston, bought sets for his six windows. One week after he had purchased them, however, he had been robbed. A burglar had climbed the fire escape and kicked in the gates.

Although there's little a board could have done in a situation like that, recounting such stories puts everyone on his or her guard. At every admissions interview, we stress to potential owners the need to know who you're admitting, whether in person or via a buzzer. Still, people are careless, leaving the front door propped open or a basement door without its double-lock secured (the latter has led to thefts from our bike room). You can remind people till you're out of breath, but sometimes they never learn. I sometimes wish we could supply everyone with a variation of the robot from the 1960s TV series Lost in Space , who could sense a threat before it happened and would invariably cry out to his young friend, "Danger, Will Robinson!"

Some years ago, in an effort to remind people about their role in security, our building had the then-manager prepare a sign that was to be posted in the vestibule. Unfortunately, we left its wording up to him, and the warning came off as strangely one-sided: "Please do not allow strangers to enter the building as you are leaving." While the intention seemed to be clear, my ever-particular grammarian father was quick to point out a flaw, a loophole that might confuse any overly literate owner: "Do not let them enter as you are leaving. What about as you are entering? Is it okay to let them in then?"

As wordsmith E.B. White might have put it, security be damned. When crafting security warnings, you can't be too careful. Or precise.

Reprinted from Habitat February 2009. For more, join our Archive >>