You may think that satnav devices are all about ensuring a swift and safe passage along the open road, but they're also about getting you from place to place efficiently.

Why shouldn't they also equate to getting there cost-effectively?, reasons Chris Hobbs of Vexia, which developed the Econav. You could save as much as £200 in six months using the Econav, he claims, meaning the device pays for itself.

"Fuel costs and carbon emissions are huge concerns for today's motorist," says Hobbs. "Using the econav system, drivers can make cost savings and have a significant effect on the environment without even thinking about it - driving efficiently can become an everyday routine."

Vexia Econav 350 Total Europe satnav

The Econav is much like any other personal satnav device. It has a good-sized touchscreen with large onscreen icons that can be pressed to access its various functions, even while driving (though you're not supposed to, of course).

Mapping information is supplied by both TeleAtlas and Navteq depending where in Europe your journey takes you. But the unusual part of the Vexia Econav is that it also has fuel efficiency information displayed whenever required.

Before you begin your journey, you prime the device with details of your car's make, fuel capacity and model and tell it how many passengers there are going to be. More than 6,000 models are listed in the Econav's database and the onscreen options adjust depending on you're driving a four-door car or an SUV, for example.

A traffic light-style onscreen display lets you know whether you're driving at the right speed and in the right gear for the road you're on. It will also let you know if you're over-revving - just the sort of detail to raise the hackles of boy racers and those stuck in interminable traffic, we're sure.

Perhaps the most useful aspect of the Econav is that it plots your journey so you can get from A to B using the least amount of fuel, using details about traffic congestion and relative road speeds to do so.

Hobbs says calculations for money-saving are based on independent statistics that suggest the average UK driving clocks up 11,000 miles a year. Another side effect of using the Econav is that carbon emissions from driving may be reduced by as much as 30 percent.

Two models of the Vexia Econav are set to go onsale in the UK next month. The UK & Ireland version of the Econav will cost £159 for the 3.5in model while the 4.3in Econav 430 Total Europe model will cost £229 inc VAT and the 3.5in 350 Total Europe satnav costs £199. All models will have European maps and automatic night and day modes.

Econav satnav onscreen information

The Econav takes into account the weather conditions and number of passengers in your car, as well as the make and model of the car, in order to calculate the most fuel-efficient route