Sat-nav applications are also available for mobile phones

Shares in sat-nav device companies have fallen substantially after Google unveiled its free live sat-nav for mobiles on Wednesday.

US firm Garmin fell 18% after details of Google Maps Navigation were revealed. Dutch firm TomTom fell 9.5% when markets closed on Thursday.

The Google application promises free real-time, turn-by-turn directions for people to follow on their phones.

The Motorola Droid will be the first mobile phone equipped with the system.

Google Maps Navigation, revealed on Wednesday, combines services including a search engine to find addresses, Google Street View for photos of locations, and live traffic data.

Other mobile sat-nav applications, such as TomTom's, can cost up to £60 to add.

TomTom's share decline wipes out all of its gains since August. Separately the company warned of lower prices in the coming months.