This is the third episode of a three-part series about sonic tactics, and it's been quite a journey. So far, I've talked about how animals use sound in the wild, from spiders doing wasp impressions to sperm whales whose calls can be deadly at close range, and how people in the past have learned to harness the power of sound on the battlefield, such as chasing off war elephants with the help of squealing pigs. We'll be taking a look in this episode at audio conflict as it exists today, and just what the future might hold when it comes to sound's growing potential for both good and harm.One of the oldest and simplest uses of sound in modern combat is one that might seem familiar to exasperated parents: playing music too loud. When used on prisoners in captivity, such treatment can amount to torture, and it's been recognized as such by the United Nations. Loud music has also been used as a police tactic for dispersing crowds, where it's had more mixed results: protesters have proven just as likely to start singing along with "Baby Shark" or Frozen's "Let It Go" as they are to run away. There can also be a cultural element to such tactical music: South Korea spent more than two years blasting K-pop songs along the border, a move that outraged North Korea so much it threatened to launch missiles at the speakers. The music only stopped in 2018 ahead of a peace summit.Audio technology is constantly changing, though, and now it can be used to hone in on more precise targets than ever before. In 2005 Howard Stapleton patented the Mosquito machine, a crowd control device that's aimed specifically at teenagers. As adults, we gradually lose our hearing thanks to the everyday wear and tear on our auditory nerves, and the first things to go are the higher frequencies. That means there are sounds children and teenagers can hear that, for the most part, adults can't detect. The Mosquito uses one of those sound frequencies – 17.4 kHz, to be exact – at 108 decibels, the same volume as a rock concert, to drive teenagers away from storefronts and public places.But, much like those crowds singing along to the music they’re supposed to hate, the Mosquito frequency’s turned out to be just as useful to the teens it’s meant to chase off. Smartphone apps have been developed since then that use the same sound as a kind of secret ringtone, so students can use their phones in class without their teachers hearing them. Want to test your ears and find out if you have the hearing of an eighteen-year-old? Check out my blog for a link to the Mosquito tone, but be sure to use a pair of high-quality headphones. Some speakers can’t even play back such a high frequency:https://www.youtube.com/watch?v=IrewnzQYrPIAs digital sound's become more and more important in our lives, our ability to direct and use it with laser-like precision has also grown. One of the most widespread and contentious uses of sound in the twenty-first century is the sound cannon or LRAD (el-rad) system, short for "long-range acoustical device." It uses interference waves to create narrow beams of focused sound that can travel up to five kilometers and was originally meant as a substitute for radio contact between sea vessels in an emergency. LRADs can relay public broadcasts, or, by switching on the siren and setting the volume to maximum, disperse crowds or subdue targets. It's been used around the world for everything from evacuation notices to scaring off animals to repelling pirate attacks on the high seas.Over the past few years, the LRAD's potential as a sonic weapon against peaceful protesters has generated controversy, and questions have been raised about whether the sound beam – which, at up to 160 decibels on military-grade models, can be louder than a jet engine – might cause permanent hearing loss. Its merits as both an audio...