By Katia MoskvitchTechnology reporter, BBC News
A new positioning system has been developed to complement or even replace current technologies such as GPS.
Made by UK defence firm BAE Systems, it relies on the same signals used by mobile phones, TVs, radios and wi-fi rather than navigation satellites.
The firm says Navsop could help find victims inside buildings during a fire and locate stolen vehicles hidden in underground car parks.
It could also be used in a war if the sat-nav system were turned off.
For now, the prototype is a big box-like piece of hardware placed in the back of one of BAE’s cars, which sports a radio antenna on the roof.
But once out on the market, it will be as tiny as a GPS dongle is today – a bit bigger than a coin – says Ramsey Faragher, principal scientist at the BAE Advanced Technology Centre in Chelmsford, about 40 miles (60km) north-east of London.