Supplying a duress alarm for personnel exposed to the public is the most cost-effective method to provide a reactive control for protecting personnel in public areas. A duress alarm is a device that allows a person to signal for help in case of an emergency, such as an attack, a robbery, or a medical condition. A duress alarm can be activated by pressing a button, pulling a cord, or speaking a code word. A duress alarm can alert security personnel, law enforcement, or other responders to the location and nature of the emergency, and initiate appropriate actions. A duress alarm is a reactive control because it responds to an incident after it has occurred, rather than preventing it from happening.

The other options are not as cost-effective as supplying a duress alarm, as they involve more expensive or complex technologies or resources. Installing mantraps at the building entrances is a preventive control that restricts the access of unauthorized persons to the facility, but it also requires more space, maintenance, and supervision. Enclosing the personnel entry area with polycarbonate plastic is a preventive control that protects the personnel from physical attacks, but it also reduces the visibility and ventilation of the area. Hiring a guard to protect the public area is a deterrent control that discourages potential attackers, but it also involves paying wages, benefits, and training costs.