Close the door.

Since 13 people died in a horrific building fire in the Bronx just days after Christmas, the phrase is being often repeated as a warning. The blaze quickly spread up the stairwell when the tenants in the apartment where the fire started fled and left the door open.

There is another way to prevent such tragedies. Make sure the front door can close on its own.

If your apartment building has three or more units, city law requires that all doors facing into public hallways be self-closing. Unless a resident props an apartment door open or disables the self-closing mechanism, the door should close automatically.

Does yours?

If not, it’s time to tell the city’s Housing Preservation and Development department. A call to 311, or a report on its website, will allow HPD to record a violation.

Unfortunately, that’s not enough. Over the last five years, HPD has issued 27,208 violations for self-closing doors. More than 9,500 of those remain unresolved — and when landlords don’t fix them little happens after a violation is issued. Unless a tenant takes the landlord to housing court, there’s not much follow-up or repercussion.

Stronger policies requiring follow-up inspection and enforcement against landlords who don’t fix the problems are needed. And the city should start a public awareness campaign to make sure everyone is aware of the need for self-closing doors, as well as working smoke and carbon monoxide detectors. While it wasn’t a factor in the Bronx fire, there were no working smoke detectors in more than half of the 73 deaths caused by fire in 2017. The more tenants and landlords know what to look for, the more they can push for changes to even the oldest buildings.

Last month’s fire, which officials say was started by a 3-year-old playing with a stove, was preventable. Efforts to enforce existing laws, follow-up on housing violations, and teaching tenants what they should look for could make a difference once a fire starts.

Start with asking the simplest of questions: Does your door close on its own?