A police officer stands with an LRAD-X 100 Acoustic Communication Device (sound cannon) during a demonstration of G20 security and crowd control measures. (Frank Gunn/Canadian Press)

By CBC News

A judge has dismissed a motion against the Ontario Provincial Police that sought to ban the use of so-called sound cannons during the G20 summit in Toronto.

While Friday's decision allows the OPP to use the devices, it also places some limits on how the Toronto police force can use them.

The details of those limitations were not known early Friday.

The sound cannons, known formally as long-range acoustical devices, are capable of emitting ear-piercing alerts that can be heard up to 1.5 kilometres away.

They can also be used to broadcast prerecorded and other messages to protesters and police.

Groups planning to protest at the G20 summit oppose the use of sound cannons, arguing the noise they emit infringes on their right to protest. Protesters also worry the devices can cause long-term hearing damage.

Police, however, argue that the cannons are essential equipment that allow their orders to be heard above the crowd noise and commotion common in street demonstrations.

While the sound cannons can cause hearing damage, police said they planned to follow both manufacturer and internal guidelines in their use, including firing alert bursts of only two to three seconds.

Read more.

Related video: Sound cannons approved for G20