Pagers are relatively inexpensive and the technology is proven. These devices should be distibuted to security minded situations, schools in context. The instructors at the least should be informed of emergencies. I think having one for each floor, much like each office space has a fire warden, would be an effective way for instructors keep an eye out for her students. Pagers are relatively inexpensive and don't require as much energy usage and signal strength as cellphones. Proven technology can help people.
The technology can be easily implemented and fielded. Right now should be the time to quickly address the issue and implement a solution. I have my doubts this simple solution is acceptable. I think companies will probably shill less tech savvy organizations into buying something overpriced but looks good just to take advantage of the situation.