You're listening to your favourite song on the radio and cruising down the highway when suddenly, your steering wheel feels shaky and your whole body starts to vibrate.
No, it's not an earthquake, it's probably a police car trying to get your attention with their new Howler system, a low frequency amplifier.
"You kind of feel it in your bones, you kind of feel it in your body as it emits that low vibration," says Insp. Ken Thrower, commander of the Calgary police traffic section.
Two years ago, Calgary Police Service started to change over their fleet with brand new black and white vehicles. All marked and unmarked vehicles come equipped with the device.
So far, 180 Howler cars are on the road. That number will reach 375 in the next two years.
"It's really an assist to the siren when the police car is in an emergency situation," says Thrower.
"Officers tell me they believe that people are more aware now when they come up to an intersection, for example."
No broken windows
According to Thrower, some people expressed concerns on social media that the device would damage property.
So the CBC went out with Calgary mother Marie-Pier Reid and her baby to test the device.
The police followed and "howled" at Reid's SUV from about five metres without disturbing her three-month-old baby.
"I hear a kind of loud and deep noise," she said during the experiment.
"It feels like they are super close, though, it feels like they are in the car with us. It's buzzing."
Not everyone can feel the device and location has a lot to do with the feeling, says Thrower.
"It depends on the environment, the conditions, the buildings around.... Maybe on Deerfoot it won't be as noticeable, I would say that downtown, it would be more noticeable to people walking by, and it's a high pedestrian area."
The frequencies have a total range of 60 metres.