Ambulances and fire engines have been given the power to stop music playing in nearby cars in Sweden so that their warning sirens can be heard.

The new alert system overrides loud music and bypasses sound-proofed car insulation so drivers will never be caught off guard by an approaching emergency vehicle. It uses the FM radio signal to jam drivers' speakers and send a voice alert that an ambulance is approaching.

Created by 23-year-old students at the KTH Royal Institute of Technology, the Evam System is being trialled in public and privately owned ambulances and fire engines in Stockholm, with plans to expand across the country later this year.

"Often drivers have only a few seconds to react and give way to emergency vehicles," said Mikael Erneberg, co-founder of Evam Systems and an industrial engineering student at KTH Royal Institute of Technology. "The optimal warning time is at least 10 to 15 seconds."