Wireless companies say they have been warned their signals could be temporarily jammed later this month both in downtown Toronto during the G20 summit and during the G8 summit in Huntsville, Ont.

The technology is expected to be used to create a so-called moving bubble of electronic silence around motorcades.

"No one will be informed of locations and times for security reasons," one wireless industry source told The Canadian Press.

The Integrated Security Unit, which is responsible for the two summits and whose members include the RCMP, Toronto police, Peel Regional police and the Canadian Armed Forces, would not comment on security plans.

"We use a lot of different techniques in ensuring security to deal with possible threats and we never share those techniques, we don't make them public," said Sgt. Leo Monbourquette, a spokesman for the unit.

The G8 summit happens north of Toronto on June 25-26 and the G20 gathering follows in the city's downtown on June 26-27.

In order to jam the signals, the RCMP must apply for an exemption from the Radiocommunications Act, which generally forbids interfering with the airwaves.

Often, the wireless industry itself receives no advance notice at all, said Marc Choma, director of communications for the Canadian Wireless Telecommunications Association.

But what interference there may be rarely lasts long, Choma said.

"The thing with jamming technologies, because a lot of law enforcement themselves, their communications are wireless as well, you'd have to try and specify what kind of frequencies that you were trying to jam," he said.

'Not precise'

"The jamming is not precise. You can't say I only want it to go one metre and three centimetres, so it could be going farther than you think. There is possibility it would interfere with other types of communications."

With cellphones and remote controls often tools of choice for setting off bombs, jammers have become a regular security tool at major national and international events.

A spokesperson for the RCMP-led Integrated Security Unit that oversaw the Olympics wouldn't say whether the technology was actually used for the Games. An exemption is often applied for just in case the power is needed, said Dawn Roberts.

But even if it had been deployed, cellphone users may never have noticed, she said.

"It may appear as a dropped call," she said.