Safety experts hosted an active shooter survival seminar in Hauppauge Friday night.

Don Longo of Radius Investigations uses props and security equipment to teach emergency tactics. A simple wedge jammed under a door can keep a gunman from entering a classroom, he says.

"The tenet is run, hide, fight," he says. "If you can get away from the shooter safely, then you run. If you can't get out, then your best choice is to hide. The third part of that is fight. If you do encounter him, you have to know what to do. You only have two choices. One is to fight him, and you really have nothing to lose. Two is to let yourself be killed."

Dozens of people attended the seminar.

Longo also says schools should have emergency response plans and practice training drills for students and teachers.