There are a number of products on the market that allow teachers to wear a panic button. If trouble arises, they push the button and an alert is sent to the the authorities and to school administrators to make everyone aware of a threat in the building. Many of these panic buttons also double as voice amplification systems and can be worn around the neck as microphones. Others are simply a clip on device
Pictured here is the Inovonics Mobile Duress panic button.