SOUTH PORTLAND (NEWS CENTER Maine) -- A Facebook post is getting national attention for claiming that a rubber wedge can slow down an active shooter.

The post comes from Katie Cornelis, of Southbury, Conn., who wrote that she got the tip from a security expert. The post has more than 1.3 million shares on Facebook.

In the comments, people have praised her for sharing the idea.

NEWS CENTER Now put the theory to the test.

WATCH:

One significant flaw ruins the theory: National Fire Protection Association code requires doors to open towards the means of egress. That means a door from a classroom opens up into the hallway, not the other way around.

Most classrooms are equipped with locks on the inside. Officer Al Giusto, a South Portland police officer embedded at the high school, said a teacher at Sandy Hook Elementary School was shot when they had to go outside the classroom to lock the door.

Federal agencies such as the Department of Homeland Security recommend that schools get rid of the handles on the exterior doors, forcing someone to go through a secure, single-point entry.

Those single-point entries typically involve a vestibule, where a person must get clearance from someone on staff before the doors are unlocked.

"Now when people come in the morning they funnel through. You see kids coming in. You look at the behavior," said Officer Giusto. "You just be nice and then see if there's anything unusual, but they have to pass you."

Giusto said that while the secure entry helps hinder threats, it is also helpful to prevent other situations that could compromise a child's security, such as divorced parents battling over custody picking up their child unnoticed, or students sneaking kids from other schools into the building.

"It's always possible. I don't think 60 years ago people thought about that, or even 20 years ago, even prior to Columbine, but it wasn't common to think, 'I'm dropping my kid off at school today, could there be a shooting?'" said Giusto.