The Insider: Guide to buying a Satnav

Satnavs have established themselves as a must-have motoring gadget over the past few years – and they make the perfect gift for petrolheads at Christmas. But with so many to choose from – and so many features to consider – it's worth doing your research before you buy. Although you can now pick one up for under £100, the very best could set you back almost four times as much.

Richard Headland, motoring editor of the consumer magazine Which?, says: "A good one will not only make it easier to find your way around, but can also help you to avoid traffic jams and keep your mileage down – which can help cut your fuel bill. Best of all, it should put an end to arguments about which route to take as you travel home this Christmas.

"Don't ditch the atlas completely, though – it's always worth double-checking the route your satnav suggests before you set off, to make sure it seems sensible."

So what should you be looking out for when you buy a satnav? The technology has come a long way over the past few years – and you can now pick up models that use voice recognition technology and which even help you to avoid heavy traffic. Generally speaking, however, the more features you want, the more you'll pay.

When Which? recently reviewed 17 of the market's most common models, the one to receive its highest ranking – the TomTom Go 930 Traffic – was also the most expensive, retailing for £370.

Although it's certainly pricey, the Go 930 has more features than any of its competitors. It uses voice recognition technology – allowing you simply to tell the machine what your destination is without taking your hands off the steering wheel – and it also has a handy "Advance Lane Warning" feature, which shows you exactly what lane you need to be in at complex junctions. It also includes European road maps as well as UK ones.

If you're looking for something cheaper, however, Which?'s second-highest scoring device – the Garmin NIM 205W – costs £140. You don't get voice recognition or advance lane warning features, but the Garmin device does come with a free traffic avoidance feature. On the TomTom machines, this feature will cost you an additional £23 a year.

While all the TomTom and Garmin models scored highly in the Which? tests, you should steer well clear of satnavs made by Blaupunkt. The two Blaupunkt models reviewed by Which? scored below 50 per cent, and were marked down for being hard to use.

Where to buy

Once you've worked out which satnav you want, the best place to head for a bargain is the web. Sites such as pricerunner.co.uk, kelkoo.co.uk and whichcompare.co.uk can help you find the retailers that are offering the lowest prices.

For example, if you're looking for the TomTom Go 930, whichcompare.co.uk will point you to the amazon.co.uk marketplace, where it's possible to pick one up for just £312 – almost £60 less than its ticket price. Froogle.co.uk, another price comparison site, reveals that you can pick one up from Handtec.co.uk for just £274.

Alternatively, you could take a visit to TomTom's website, tomtom.com, where they're selling refurbished satnavs at a 40 per cent discount to their regular price.

The Insider is written in conjunction with the consumer group Which?. For more information on the best satnavs, listen to the latest Which? podcast at www.which.co.uk/podcast or visit www.which.co.uk/satnavs. To get three issues of 'Which?' magazine for £3, call 01992 822 800 and quote INADVICE.

Before you buy: Five questions to ask

* Does it have voice recognition technology? This allows you to set your satnav without taking your hands off the wheel. Only a handful of devices currently have this great safety feature.

* Does it have a traffic avoidance tool? Most devices give you the option of paying an annual fee to have this feature added to your satnav, but a handful offer it for free.

* Can I use it in continental Europe? A small number of UK satnavs also have maps for other European countries – perfect if you regularly take driving trips across the Channel.

* Will it tell me what lane I need to be in? Some satnavs have an "Advance Lane Warning" feature, which tells you where you need to be positioned on the road as you approach complicated junctions.

* Will it warn me about speed cameras? Most satnavs have the option of including a speed camera monitor, for an additional annual fee. A small number of devices offer this service for free.