Sat nav reviews: FAQs

Person using sat nav

Sat navs use GPS to find where you are

How do sat nav systems work?

Sat nav systems use a global positioning system (GPS) satellite receiver to calculate their position on the Earth's surface. This is overlaid onto a local road map showing your position to within 10 metres. Sat nav software calculates the 'best' route between two points, using average road speed data with other parameters.

All sat nav systems give voice instructions for route guidance, for example, 'Turn left in 300 yards'. Sat navs let you input your destination as a full postcode, or house number, street and town name. If you don't know the house number, the sat nav will take you to the postcode or the street so you can be reasonably precise. The best sav nav systems have clear screens with clear visual and audio instructions. They're also easy to set up and programme in a destination.

Find the best sat nav system for you with our Best Buy sat navs.

How should I prepare to use my new sat nav?

  • Read your sat nav system's quick start guide – most have one. 
  • Sit in your car and consider the best position for the sat nav. You’ll need to read the sat nav at a glance then resume full concentration on the road.
  • Most sat nav systems include a support bracket, which attaches to the windscreen using a powerful sucker.
  • Position the sat nav as low down as possible, so it doesn’t obscure your view of the road or the car's instruments. Make sure the sat nav's cable reaches your power point without interfering with other controls.
  • Enter as much detail about your target destination as possible into the sat nav. The postcode is good, but if not, you’ll need the (correctly spelled) road name and number, town and maybe county.
  • Your sat nav may not find a very newly built address if the map is out of date. Consider whether there’s an older address nearby for your sat nav to target instead.

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Do I need to install an aerial for my sat nav?

No. All portable sat navs include an integral antenna to receive the GPS signal that gives the sat nav system its location.

Some sat nav makers offer an optional external antenna, which can improve the sat nav's performance, particularly in built-up areas.

Can sat nav systems be used in any car?

Generally sat navs can be used in any car, though we've heard of some cases of poor GPS reception in vehicles with heated front screens. Try the sat nav out in your car before you buy.

What route options do sat navs offer?

Most sat navs let you select from a range of options, eg the quickest or shortest route, or choose via a particular waypoint or one avoiding motorways or toll roads.

If I have a sat nav, will I still need an atlas?

Buying a sat nav usually means that you don't need an atlas as sat navs are usually very reliable, but keeping an atlas in the car anyway may be a good idea as a back-up.

As some sat navs don't give provide live traffic information, tuning into radio traffic websites and checking the Highways Agency websites – and before or during your journey could also be sensible.

Should I believe my sat nav's estimated journey time?

Check the sat nav's estimated time and predicted mileage. Add in time for refreshment breaks and fuel stops and leave with plenty of time to get to your destination.

It may be tempting leave with exactly the time the sat nav estimates it will take, but in Which?'s experience, sat navs' estimated times tend to be quite optimistic.

Can sat navs detect speed cameras?

Yes, most of them can. They can detect fixed and in some cases mobile speed cameras. Audio and sometimes visual signals are given on the screen to warn you that one is coming up.

Are sat nav systems distracting to use?

Supporters claim sat nav systems take the stress out of driving by guiding motorists quickly and safely to their destination. Which? has reviewed, tested and compared lots of sat nav systems, and some are more distracting than others.

The best sat nav systems for reducing distraction have wide screens, clear, simple and timely visual and audio prompts, easy-to-navigate menus and simple operational features.

Map of europe

Some sat navs come with European mapping installed

Can I take my sat nav on holiday abroad?

The majority of sat navs come installed with UK and Ireland mapping only, but you can easily buy the same model with European maps also installed, for a little bit extra.

Even if you have just buy the UK and Ireland map version, you can buy and install European and other maps later, if you wish.

Assuming you have the map for the country you're in, the sat nav should work in any car – including a hire car.

What is TomTom HD Traffic?

HD Traffic is TomTom's live traffic avoidance service. See 'Sat nav live traffic' for more information.

Inserting an SD card to a satellite navigation device for map updates

Maps can be updated by fitting SD cards to the sat nav

What about sat nav map updates?

To account for road network changes, sat nav manufacturers bring out new maps – up to four times a year. Points of interest such as petrol stations are also updated. Portable sat nav systems can usually be updated through connection to an internet-connected PC, or you can buy a memory card with the map update.

Most phone-based sat navs can download updates through their normal mobile phone connection. On some systems, you can update corrections to your map through the satnav itself. To update a factory-fitted sat nav system you usually need to buy a data DVD from a franchised car dealer.

Updating your sat nav's maps can be expensive. You don’t need to do it though – many people get by on old maps – but of course you run the risk of the sat nav trying to direct you down a road that no longer exists, or a roundabout that is now a crossroads. Old maps can sometimes get you a bit lost.

The price for updates will depend on the coverage you require (eg UK and Ireland will be cheaper than Europe). A new DVD for a factory-fitted sat nav system will cost between £150 and £200. Portable sat nav system mapping updates range from about £20 upwards.

How do I make sure using my sat nav doesn't compromise my driving safety?

  • Familiarise yourself with your route prior to setting off.
  • Never try to alter the sat nav's settings while driving. If you need to change anything, find a safe place to stop where you face the least risk.
  • Ensure your vision isn't compromised by where you attach your sat nav system.
  • Remember sat navs are fallible and are only there to aid you. Use your common sense, and don’t blindly follow sat nav directions that may be dangerous or incorrect.
Thief breaking into a car to steal a sat nav

Keep your sat nav safe

How can I stop my sat nav making my car
a target for thieves?

Recorded thefts of sat nav systems are increasing. Follow these tips to keep your sat nav safe.

  • Take portable sat nav systems and their mountings with you when leaving the car.
  • Wipe away any suction pad marks the sat nav leaves on the windscreen or dashboard, as thieves will look for these.
  • Avoid leaving the sat nav in the glove box – thieves usually check there first. Consider leaving the glove box open to show the sat nav hasn't been left in the car.
  • Record your home address under another name to stop a thief from simply following the sat nav's directions and ransacking your house when they know you’re out.
  • Mark your sat nav using special security markers.
  • Note down the sat nav's make, model and serial number and keep the details somewhere safe – not in the car.
  • Consider recording your sat nav's details on a commercially-available asset register such as

Is my sat nav covered by my car insurance?

It’s important to check with your insurer whether your sat nav is covered. Many distinguish between accessories fitted as standard and those added later.

Even if your sat nav is covered by your car insurance, it may not be worth making a claim. 

Policy excesses may include the first £100 of a claim – almost as much as a cheap sat nav system can cost – and the resulting loss of your no-claims bonus can be more expensive than any minimal recompense you may receive.

An image of walking mode on a mobile phone based sat nav

Many dedicated sat navs and mobile phone sat nav apps have a walking mode

Can I use my sat nav when out walking?

Yes. Portable sat navs are a little bulky to carry around with you while walking, but if you can put up with that bulk they work fine out of the car as well as in. Many have a walking mode which is worth seeking out. Battery life is limited to a few hours, so they're not really practical for very long walks. Of course, sat nav apps on mobile phones are a little bit more practical due to their lower weight and smaller size.

Have you tested any sat navs that are suitable for larger vehicles?

The Snooper Syrius Proline with Truckmate allows you to key-in your vehicle dimensions and weight, to avoid low bridges, narrow roads and weight limitations.

We tested it using some typical stats for an articulated lorry, a small truck, a double-decker bus and a large van. We asked the Snooper to direct us to locations with known restrictions along the most obvious route.

The system mostly avoided taking us under bridges that were too low, either by routing us round them or by refusing to calculate a route. This latter option wouldn’t have been helpful had we genuinely needed to get around the bridge. 

Some bridges weren’t marked on the sat nav mapping, and several times it directed our smaller vehicles to avoid bridges unnecessarily. For one bridge in Scotland, it managed to avoid the chosen bridge, but re-routed us under a lower one!

When testing for width restrictions, there were more examples not marked on the map, and it seemed particularly to struggle with the large van – directing us via roads too narrow for safe progress.

From our testing, while major routes seem reasonably well accounted for, minor routes are not well covered, so the driver would need to check the local restrictions before setting out.

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