New York, NY – I’ve been complaining for months that my new neighbor’s cigarette smoke is going to kill me, so when our carbon monoxide alarm went off the other night at 10:30, I carried it out to my husband and, waving it angrily. “See? See? It’s so bad, it’s even setting off the monitor!”

He shrugged. I took out the batteries and went to sleep.

Three hours later, we were woken by persistent pounding on our front door. When we opened it, three firefighters in full gear entered with a handheld device blaring. As the numbers on the detector ticked higher and higher, one of the men said: “Wake up your children. Open all the windows. Your apartment is filled with carbon monoxide.”

Emmett is 4 and woke on his own seconds later, disturbed by all the noise. Luka is 13 months. He’s an adorable little baby with a heart-meltingly sweet smile who has just started taking his first, hesitant steps. He sleeps right outside our bedroom in our ground-floor apartment — directly over the boiler, the same boiler that was

spewing deadly fumes into the air.

That’s what keeps going through my mind, even days later: how the baby would have gone first. If the Fire Department had arrived later, maybe the rest of us would have been fine, but Luka would have died in his sleep.

In the chaos of the moment, clutching the children while trying not to scare them, opening windows, tuning out the screeching alarm, it took us a while to understand that our upstairs neighbor had called the Fire Department. Her carbon monoxide alarm went off, so she called. I’m still in awe of the simplicity of her reasoning. Nothing is that straightforward to me, even matters of life and death. I’m one of those idiots who worries about wasting the firefighters’ time with a false alarm.

After every window was opened, it took more than a half hour for all the carbon monoxide to dissipate. Once it did, the firefighters closed the windows and waited another 15 minutes to make sure the apartment wouldn’t fill up again. It didn’t. With the boiler turned off, the problem had been temporarily solved. The Fire Department took off, and we were left with one peacefully sleeping baby, one anxious little boy and our overwhelming stupidity. That the carbon monoxide alarm had detected actual carbon monoxide was never on our radar. If we hadn’t chalked it up to our chain-smoking neighbor, we would have assumed the device was broken.

The firefighters suggested that the carbon monoxide was caused by an improperly maintained boiler, but the culprit turned out to be a blockage in the chimney caused by construction on the building next door. An unmoored tarp had knocked off the cap that prevents debris from falling into the chimney.

I’ve always felt vulnerable living in an apartment in part because you’re dependent on the thoughtfulness of other people. You have to trust them to turn off their irons and blow out their candles. But the truth is, you are vulnerable living in the world. Any tarp at any moment can impact your fate. Impact — but not decide.

Carbon monoxide alarms work. New York City law requires every dwelling be equipped with a carbon monoxide detector that has the Underwriters Laboratories (UL) Mark and complies with the requirements outlined in Standards UL-2034. Furthermore, the New York Fire Department recommends that you have one detector on each floor and in each bedroom if you sleep with the door closed. You should also have one near any fuel-burning appliances, although not within five feet.

The New York Fire Department prefers a digital device with a readout that tells you the actual CO level and suggests you get a new one every four to five years. Make sure your alarm works by checking it at least once a month. The Fire Department advises replacing the battery every time you switch your clocks for daylight savings. (Repeat after me: Change your clock; change your battery.) All this information can be found on NYC.gov (PDF).

The most important thing, of course, is heeding the alarm if it sounds. Stay calm, silence the device, ventilate the space, call 911 and evacuate. Don’t ignore it. We were lucky, but there’s no need to rely on luck.