If troops spot someone suspicious approaching them, they can use the Long Range Acoustic Device to send a warning message. It fires narrow beams of sound waves that can be heard clearly from 300 meters (about a thousand feet) away. Crank up the power, and it can emit a warning tone so loud that anyone in its path would have no choice but to cover their ears and run.
The manufacturer doesn’t like to call these devices weapons, even though they’ve been used to repel pirates. Cops used them to harass protesters at the G20 summit in Pittsburgh this year.
Photo courtesy U.S. Marine Corps