With the terror threat from ISIS growing, many of us rightfully warn of a “pre-9/11” mindset of lax government security. But that warning also applies to private citizens and business owners, who can do more to keep themselves safe instead of waiting for the state to step in.

The morning after 9/11 my phone began ringing off the hook. The calls were from CEOs of major corporations and banks and building owners and managers around New York City. Every request was the same: “We need to beef up our security. Can you send help quickly?”

I did — providing armed, trained professionals with law enforcement backgrounds at many of these locations. My company installed magnetometers in commercial building lobbies and searched the bags and packages of each person that entered the premises, employees and visitors alike. People thanked us, even after waiting on a line to enter.

At some locations, we deployed dogs trained in explosive-device detection. I had personnel stationed at loading docks and parking garages to search cars. We made what are referred to as “soft targets” — landmark buildings, commercial properties, residential locations — safer.

As the months went on, the calls began coming in again. This time the callers were asking, “Can you cut down on our security?” “Why?” I asked. The answers were all the same: “We’re trying to cut costs; it’s too expensive.”

These cutbacks soon became the norm nationwide. “Could you just give me an unarmed security guard to stand in my lobby? You know, just to sign people in.” “Can you give me that service for a dollar less per hour than what you’re charging?”

I found myself bargaining with these real estate titans over a few dollars. But I also couldn’t pay good, solid, reliable personnel what they deserved for the price that landlords and management were demanding. And forget about armed guards.

So here we go again.

Just over a week after ISIS terror attacks paralyzed Paris, Brussels is on lockdown. FBI Director James Comey says ISIS is in American cities now, too.

Safety has once more become a primary concern for commercial and residential buildings, and now the calls for enhanced security measures are starting to come in again. But have we learned anything from recent history? Are we just going to ramp up security for the next six months or a year?

The question, essentially, is this: Are we just going to react to such atrocities, or are we going to be prepared to prevent them?

I applaud NYPD Commissioner Bill Bratton for recently speaking about security concerns at soft targets. The new NYPD Counter Terrorism Response Unit will operate under the belief that terrorists intend to kill anyone and everyone they can as quickly as possible. Consequently, police officers won’t take the time to negotiate; they’ll act efficiently and without hesitation to save lives. The private sector now needs to step up and begin to do the same.

We can never eliminate a threat; however, we have the ability to minimize the carnage. The presence of enhanced security with armed, former law enforcement personnel at soft target locations is essential for the speedy preservation of human lives when these animals pay us a visit. A guard with a pen and a sign-in book won’t be enough to stop an active shooter, whether it’s a terrorist, a disgruntled employee or a party to a domestic dispute. There will be no time to call for backup.

It’s time to learn from recent tragedies so that we can impede future violence.

The threat that we face must be dealt with on a day-to-day basis. With the holiday season upon us, we’re especially vulnerable. Millions of tourists will be drawn to the city to see the Rockefeller Center Christmas tree, the Radio City Christmas show and the Thanksgiving Day Parade. ISIS will view this influx of civilians as a perfect opportunity to spill gallons of American blood in our country’s greatest city.

An attack can come at any time in any place, and the private-security industry must rethink what we can offer to keep American citizens safe not just for a day or a month or a year — but for the long term. For as long as we must.

An alarm has been sounded, and here in America — and especially in New York City — we’re facing the biggest ongoing terrorist threat in our history. We must meet this danger with all the resources we have and not let up until we defeat this ISIS threat.

Bo Dietl, a retired NYPD detective, is CEO of Beau Dietl Associates.