Communicate and a non lethal weapon..

LRAD (Long Range Acoustic Device)
The Long Range Acoustic Device (LRAD™) is a breakthrough, highly-directional hailing and warning system designed to communicate with authority, affect behavior, and help determine intent up to 300 meters away. LRAD is a communication device that is:
All-Weather
Man-Portable
Highly-Directional
LRAD offers the ability for:
Police to provide clear direction to gatherings and crowds
Officers to serve warrants from a safe distance.
Fire crews to communicate to potential victims in tall buildings or hard to reach areas.
Prison Guards to determine intent of groups and clearly control a riot without munitions
Maritime Vessels to clearly and forcefully communicate with small vessels that pose a threat.
Security Personnel to communicate in host nation language from a safe distance for checkpoint control
Airport Managers to scare away birds from roof tops and air fields with a directional transmission
Border Patrol Agents to clearly give warnings from helicopters to people on the ground with clarity over turbine noise
Hazardous Response Team Leaders to communicate with people in hazardous areas warning innocent bystanders to stay away in any language

http://www.audionation.co.uk/products/military/lrad.html