All schools now have buzzers at the front door that are connected to cameras at the office, and school doors are locked. The weak link is who is on the other end of the camera... people are afraid to question others about why they need to be there and to avoid conflict they just let everyone in who rings the buzzer.
“All schools now have buzzers at the front door...”
Not around here they don’t.
In hot Arizona, each school room opens to the outdoors like an outdoor shopping center.