How GPS works

GPS (Global Positioning System) is a navigation technology that provides precise time and location data by using 24 NAVSTAR (Navigation Satellite Timing and Ranging) satellites. Each satellite completes one orbit of the Earth every 12 hours. They are positioned at an altitude that allows them to cover the same ground once every 24 hours (minus four minutes).

Each satellite carries an extremely accurate atomic clock and transmits both its position and a time signal, which can be picked up by a GPS receiver. Since a GPS unit can receive data from multiple satellites, and since each satellite provides information that is appropriate to its own location and distance, the GPS unit performs the necessary calculations and arrives at a position fix accurate to within about 50 feet. Many factors can have an impact on accuracy, including atmospheric conditions, buildings, tunnels and heavy foliage. However, reviewers say that the latest SiRFstar III-based receivers greatly minimize those issues.

Handheld GPS vs. Auto GPS

GPS receivers for the outdoors market and for the automotive market are two different animals, although both can do double duty. Outdoors-oriented GPS receivers are made to resist the elements -- most are rubberized and water resistant. Handheld GPS units are also meant to be lightweight and easy to hold with one hand. They have smaller screens than auto GPS receivers do, and the screen isn't always in color. Handheld GPS receivers also emphasize battery life.

Auto GPS receivers are portable, but you wouldn't want to take them camping. They aren't water resistant, and because of the large screen, they are much heavier than a handheld GPS (although the average weight is less than half a pound). The big screen also saps battery life. Most auto GPS receivers can plug into a cigarette lighter. Auto GPS units come with highway maps and give audio directions. Handheld models sometimes only come with the most basic maps, and some don't come with maps at all. Auto GPS receivers also come with a windshield or dash mount, while most handheld GPS units don't. (Note that mounting on windshields isn't legal in all states.) Reviewers note that portability is a big deal, because GPS units mounted on dashboards or windshields are enticing to thieves.

Another option for in-car navigation is using a Bluetooth GPS accessory with a laptop or PDA. Some PDAs come with an integrated GPS antenna, while others can accept an accessory receiver. Laptops have a larger screen than an auto GPS, and they have lots of hard-drive storage for maps, but they aren't easily installed in your car, and work best if you have either a copilot or software that gives audible directions. Otherwise, they are unsafe to use.

Experts say that aftermarket GPS units are better and cheaper than those that can be factory installed in new cars. The factory-installed units can't be updated and can only be used in one car. But factory-installed GPS units have two advantages: they offer a clean, integrated installation and they are much more difficult to steal than aftermarket auto GPS units. This report covers aftermarket units; the factory-installed units are rarely reviewed.

Best auto GPS receivers

We rarely encounter a product that reviewers say dwarfs the competition as much as the Garmin nuvi 660 auto GPS (*est. $550) . GPSLodge.com's Scott Martin sums up the consensus when he writes, "The Garmin nuvi 660 is a great GPS unit…the best I have used."

Reviewers note a number of reasons for their infatuation. For example, Martin says that the nuvi 660 auto GPS is "chock-full of features without adding clutter or confusion to the interface." Even the functionality of the integrated MP3 player is well thought out, pausing the music, announcing the direction, then resuming the music. Martin commends the "great functionality" and small form factor. In his review for GPSTracklog.com, Rich Owings likes the "user-friendly design and intuitive interface." Christian Harris of BIOS magazine likes how the super-bright, white, backlit screen looks great in his car and that the screen is also easily viewable in sunlight. He also raves about GPS reception and features.

Reviewers unanimously agree about the Garmin nuvi 660's assets and its one major disadvantage -- the high price. Features include a bright, backlit touchscreen, an FM transmitter to play MP3s through your car stereo, and Bluetooth. A three-month subscription to FM TMC Traffic is included; after that, one-year renewals are available (*est. $60). TMC stands for Traffic Message Channel -- it's a service that provides real-time traffic alerts for about 50 U.S. markets and is used by the satellite radio networks.

The Garmin nuvi 680 auto GPS (*est. $650) is identical to the nuvi 660, except that it uses a more full-featured traffic service. The Garmin nuvi 680 is bundled with a one-year subscription to MSN Direct service (additional years cost *est. $40). The service is available in 120 metropolitan areas. In addition to traffic alerts and rerouting, MSN Direct service transmits current local gas prices, weather conditions, alerts and forecasts along with local movie show times.

While PC Magazine likes the MSN Direct service, the reviewer inexplicably fails to address the safety considerations of using a touchscreen to access information while driving. Blogger John Pozadzides at One Man's Blog prefers the nuvi 660 over the nuvi 680 based on poor service he received from MSN Direct with a previous product. However, PC Magazine says that the two traffic services are comparable. As MSN Direct currently serves more than twice as many metropolitan areas as FM TMC, your choice between the nuvi 680 and the nuvi 660 may be dictated by where you live. Note that you can also use the FM TMC service with the nuvi 680.

The older Garmin StreetPilot c550 auto GPS (*est. $360) is a step down in price, but still highly regarded by reviewers. Laptop magazine selects it as an Editor's Choice. Reviewer Troy Dreier says the navigation quality rather than the features is the reason to buy the c550.

The major distinction between the StreetPilot c550 and the Garmin nuvi 660 is screen size. The c550 has a standard 3.5-inch screen with an antiglare coating that reviews say makes it easy to read in bright sunlight. Meanwhile, the Garmin nuvi 660 has a larger 4.3-inch screen, but the weight is about the same. Like the nuvi 660, the c550 has preloaded maps of North America, an MP3 player, specific street text-to-speech functionality, and a three-month subscription to FM TMC Traffic. You can use the StreetPilot as a speakerphone when paired with a compatible Bluetooth phone.

The Garmin StreetPilot c580 (*est. $410) is the step down from the Garmin nuvi 680. It is identical to the c550, but uses the MSN Direct service instead of FM TMC traffic service. CNet.com ranks it as the second-best auto GPS unit, topped only by the nuvi 660. CNet's Bonnie Cha says it provides accurate driving directions.

TomTom is Garmin's big competitor in this market. The new TomTom GO 720 (*est. $450) is generating plenty of buzz with its new features. You can update a map yourself, or download updates suggested by other owners -- a unique interactive approach to map updates. The TomTom GO 720 comes with a USB docking cradle. Most reviews gush about the TomTom GO 720. TrustedReviews.com gives it perfect scores for features, usability and value. Reviewer Jonathan Bray concludes, "The TomTom GO 720 is the most capable, feature-packed, easy to use and innovative in-car sat-nav device on the market today." GPSLodge.com, PC Magazine, GPSReview.net, CNet.com and PC World are only slightly less effusive in praise, yet each of these reviewers has a different criticism of the TomTom GO 720.

As always, GPS magazine employs the most comprehensive testing and publishes the most comprehensive review of the TomTom GO 720. In spite of citing a lengthy list of virtues, the review concludes "The GO 720 has a long list of great features that just might keep you distracted long enough not to notice that the core functionality of the GPS doesn't work that well." The review goes on to say that the GO 720's routing engine is inferior when compared to Garmin or Magellan, and adds that "the GO 720 consistently chose the worst route in my testing." Both GPS magazine and PC World mention that sometimes the GO 720 gives directions too late.

Along with a 4.3-inch widescreen (touchscreen) display, the TomTom GO 720 has all the popular GPS features and more. Those include Bluetooth and an SD card slot. You can use the integrated speaker or the FM transmitter to broadcast to your car stereo system. The unit includes an MP3 player, and you can connect an Apple iPod if you prefer.

The Garmin StreetPilot 2820 (*est. $690) is recommended by GPSInformation.com, but it is one of the units GPS magazine says to avoid because it has the older GPS chipset. GPSReview.net says the StreetPilot 2820 auto GPS is much bigger than the nuvi car GPS units, yet Garmin markets it for motorcycles as well as cars. You can buy an add-on antenna to receive XM satellite radio (subscription required). That capability distinguishes the StreetPilot 2820 from the Garmin nuvi line of auto GPS devices.

If you need a larger display, consider the Garmin StreetPilot 7200 (*est. $750) . This is an older model that again uses an older chipset. The newest reviews are more than a year old, so they have minimal validity since, as experts note, technology continues to improve. The biggest reason to consider the 7200 auto GPS is its 7-inch display – twice the size found in most units, and the largest in a consumer GPS product. That may make the StreetPilot 7200 a good choice for RVs and buses.

If you don't want or need traffic alerts, or live in an area with no service, some reviews still recommend the Garmin nuvi 660 auto GPS. Otherwise, reviewers recommend the TomTom ONE or Garmin nuvi 350 (with MP3 playback), which are covered below.

Other high-end auto GPS receivers don't fare nearly as well. For example, we found two recent reviews of the Magellan Maestro 4050 (*est. $470) that fall short of unqualified recommendations. The Magellan RoadMate 800 (*est. $370) , Rand McNally GPS Navigator (*est. $360) and ViaMichelin X-970 (*est. $350) are among other higher-end units that don't score as highly as the Garmin nuvi auto GPS.
Budget auto GPS units

Auto GPS receivers are expensive, but prices have been dropping rapidly -- at least 25 percent in the last year. Some of that is the result of new manufacturers offering less expensive entry-level car GPS units. None of those fare particularly well in reviews, but they do have the effect of dragging down prices as more established manufacturers are forced to compete. In the current market, nothing over $400 can be considered budget, and entry-level-yet-capable auto GPS systems can be had for around $200.

The TomTom ONE (*est. $210) is handily the best budget car GPS unit. In fact, many reviewers believe it is the best pure auto GPS unit on the market. The price has dropped by more than 50 percent since the product was new. GPSReview.net summarizes, "It is really hard to go wrong with the TomTom One." Note that TomTom has revised this product a couple of times without changing the name. To take advantage of the minor upgrades, get a recently manufactured unit if possible.

Although it's a matter of personal taste, most reviewers love that the TomTom ONE is just a GPS receiver. It won't play MP3s or warm your coffee through a USB connection. It does have Bluetooth connectivity, but is not capable of hands-free cell-phone calling. Reviewers also love that the TomTom ONE is a very capable auto GPS unit, with Laptop magazine’s Billy Ristle saying, "While there's no such thing as a one-size-fits-all GPS device, TomTom's One comes really close." One disappointment cited by GPS magazine is that the TomTom ONE uses Tele Atlas mapping data, while all competing brands use NAVTEQ maps. In its tests, the site found that the TomTom ONE "simply didn't have the addresses of many locations that other NAVTEQ-powered GPS units did."

Editors at Lordpercy.com, CNet.com and PC World concur that the TomTom ONE is a good value. At PocketGPSWorld.com, reviewer Darren Griffin asserts, "In this price range there is nothing to match it." Reviewers are also in agreement about the TomTom ONE's easy portability. The unit has a 3.5-inch touchscreen, but thanks to a slim form factor, it weighs only 5.6 ounces.

That advantage doesn't extend to the TomTom ONE XL (*est. $300) . With a 4.3-inch display and higher price, the TomTom ONE XL literally and figuratively requires deeper pockets. Most reviewers agree that the super-sized version of the TomTom ONE isn't as good as its smaller sibling. We found two reviews that strongly recommend it, two that clearly do not recommend it, and five mixed reviews.

Most reviewers prefer the portability of the basic TomTom ONE to the bigger display on the TomTom ONE XL. When it was introduced, the TomTom ONE XL lacked text-to-speech capability, the TomTom has now added that feature. Editors at enthusiast site LordPercy.com strongly prefer the TomTom ONE to the TomTom ONE XL, which "despite its excellent screen, has issues with the poor mounting system and battery [life]."

Reviewers often compare the TomTom ONE with the Garmin nuvi 350 auto GPS (*est. $370) , but the TomTom unit's price has dropped more rapidly and more recently. Some say the nuvi 350 is easier to use. GPSReview.net explains that it's simpler because it has little advanced routing functionality compared with the TomTom ONE. The Garmin nuvi 350 is an older unit, and was once considered the best GPS system available. So, at its current price, the nuvi 350 auto GPS is instead being hailed as a very capable budget alternative.

Reviews say navigation on the nuvi 350's 3.5-inch touchscreen is easy and intuitive. The 2-gigabyte flash memory leaves a full gigabyte available for the user to add photos, audio books or MP3 files, and you can listen to music or a book while navigating. CNet.com's review notes the Garmin's "massive" database of points of interest. You can plan multi-leg trips, along with a wide variety of other trip planning. The nuvi 350 includes text-to-speech capability, so audio directions include actual street names instead of merely "turn left." That is the most important feature, and one that distinguishes it from the TomTom ONE. The unnamed reviewer at GPSReview.net writes, "If you are looking for your first GPS device and want something extremely simple to use, the nuvi 350 should be on your list of devices to consider. If your navigation needs are a little more sophisticated, you might want to consider a device with more routing features such as a TomTom One."

A few GPSReview.net readers have recently complained that they bought nuvi 350s that had glare problems. Site operator Tim Flight confirmed with Garmin that the company switched display suppliers. Because of that issue, we encourage you to buy from a dealer with a liberal return policy should you choose this model.

The Garmin nuvi 200 (*est. $240) is the base model in the nuvi line. It is recommended in reviews, but the older nuvi 350 has many advantages. Those include text-to-speech, longer battery life, MP3 playback and FM TMC traffic compatibility.

In our last revision of this report in June, we identified the Magellan RoadMate 2000 (*est. $215) as the best unit in its price range. Since then, prices for higher-end competing products have dropped into the RoadMate 2000's price range, while the RoadMate 2000's price has remained largely unchanged. Market factors infer that the RoadMate 2000 is due for a big price drop, or it will soon be replaced in Magellan’s product line. If you find the RoadMate 2000 at a price that is much lower than the TomTom ONE's, the RoadMate 2000 is a viable budget alternative.

The RoadMate 2000 doesn't have advanced navigation features, such as text-to-speech for announcing the names of streets (it can only announce turns, not street names). It also lacks features found in more expensive units, such as MP3 playback, Bluetooth and traffic advisory service. The POI (points-of-interest) database has just 1.3 million listings, compared with six million in more expensive car GPS units. But, as GPSReview.net notes, "at the advertised price, you wouldn't expect to get those features and many people never use any of those features." Included are NAVTEQ maps for 48 states and a 3.5-inch color touchscreen display. Reviews say the display is easy to read in sunlight and automatically adjusts for night viewing. The RoadMate 2000 auto GPS can reroute you around traffic delays, and it will remember addresses and POI routes for reuse.

Performance receives mixed notices, but reviewers agree that it's good in urban areas. PC Magazine's Craig Ellison says that the menu system "can be aggravating at times," but Jess Ross Grogan at GPSInformation.net finds that it "is generally very easy to figure out in no time." However, Grogan does say that while the routes created by the RoadMaster 2000 are accurate, they aren't always the most efficient in either time or miles. Still, the opinion of most reviewers is echoed in Ellison's comment that the RoadMate 2000 auto GPS "is a good choice for the value-conscious consumer."

Reviewers clearly believe that older budget models that were originally sold for high-end prices offer much better value than those made to sell for less than $350. Companies that have well-known brand names but are new to selling GPS devices consistently receive mixed or unflattering reviews. The Delphi NAV200 (*est. $225) and LG LN740 (*est. $330) are typical examples. Both units are reviewed by a couple of sources and earn average or lower ratings.
PDA-GPS combos

If you already own a Bluetooth-enabled Palm or Pocket PC PDA, you can turn your PDA into an auto GPS with a Bluetooth GPS plug-in. These are compact and lightweight. Since screens on PDAs are larger than those on handheld GPS receivers, they are more adaptable for use in a car, and some PDAs have screens that are as large as those in auto GPS units. You can also choose a PDA that has built-in GPS. These models don't usually come with accessories like a cigarette-lighter power adapter or a windshield mount, so count on paying extra for those items. Alternatively, reviewers point to a new product that is a full-fledged auto GPS unit as well as a PDA and multimedia player.

The HP iPAQ rx5900 Travel Companion (*est. $410) is marketed to people who want one portable device instead of three or more. It uses TomTom's software, which is highly regarded by reviewers. It has an integrated SiRFstar III GPS receiver with an omnidirectional GPS antenna. The unit runs Windows Mobile 5.0 and mobile versions of Microsoft Word, Excel, PowerPoint, Windows Media Player and Internet Explorer, and additional HP software. The iPAQ rx5900 comes with a car dock and car charger and has integrated 802.11b/g wireless networking, Wi-Fi and Bluetooth. The core hardware includes a 400MHz processor, 64MB of RAM and a 3.5-inch antiglare touchscreen.

Pocket-lint.co.uk, Laptop magazine and CNet.com all give the iPAQ rx5900 very favorable reviews. The one criticism expressed by all three is short battery life, with Laptop magazine saying the backlighting is a battery hog. On the plus side, Pocket-lint.co.uk says that the iPAQ rx5900 is the first hybrid PDA/GPS unit "that really works," adding that the "combination of HP and TomTom's knowledge makes it more than the sum of its parts." Laptop magazine adds that the iPAQ rx5900 features top-of-the-line GPS software, all of the productivity and connectivity features you need and the ability to provide a soundtrack for your trips. Note that because of HP's practice of using model numbers to track sales of their products by channel, you'll typically see the iPAQ rx5900 identified as the iPAQ rx5915 in brick-and-mortar and online stores.

Note that Microsoft has released a new version of its Windows mobile operating system, Windows Mobile 6, and the HP iPAQ rx5900/rx5915 is not upgradeable according to reports we've seen. However, reviews say that the while the new operating system offers some nice improvements over Windows Mobile 5.0, the changes are far from earth-shattering. These PDA/GPS units -- and a host of other Windows mobile 5.0 products -- remain current for the present.

HP just released the iPAQ 310 (*est. $450) , expected to reach stores by the end of October. A couple of sources (not HP) speculate that the iPAQ 310 will replace the iPAQ rx5900, but the two products are distinct enough to coexist in the market. The new iPAQ 310 is less functional as a PDA. It uses a proprietary operating system created by HP instead of Windows Mobile. It has a bigger display (4.3 inches) and twice the RAM (128MB). Additional features include text-to-speech and zoom capability. It includes a 2GB SD card slot and a mini-USB connector. You can download trip plans. For those interested, Notebooks.com has a video demo (see Best Research below).
Important Features: Auto GPS

Here's what experts say to look for when considering a GPS unit. Your considerations will vary a bit depending on whether you are looking for a unit for use in the car, a camping/hiking model or one to use for both purposes.

    * Quantity and quality of maps is critical. Furthermore, they must be up to date (or updateable) unless you will only drive in extremely mature cities like New York or San Francisco. Built-in and detailed road maps of your area of interest are an essential feature of a good automobile GPS receiver. The ability to upload maps with a USB cable or memory cards is also desirable. Some units have SD card slots.

    * Automatic destination routing is a standard feature on any good car navigation GPS. Some inexpensive units can only handle point-to-point routing, while more sophisticated auto GPS models can handle multi-segment trips.

    * Look for text-to-speech capability. Instead of just giving an instruction to "turn left at 100 feet," models with text-to-speech can pronounce the street name ("turn left at 100 feet on Main Street"), giving you better information and reducing the need to look at the screen.

    * Make sure the unit you select is capable of being mounted neatly and securely on your dashboard. Nearly all models come with the proper hardware, but it may be an additional cost accessory with some. Experts point out that you must be able to mount the unit where it won't interfere with airbag deployment. Otherwise, the unit could be blasted into you or a passenger. Note that some states do not allow windshield mounting.

    * Consider multimedia features. Many units play MP3s and can store photos. Some models play through integrated speakers, while others have an FM transmitter to play through your car stereo. Although wireless FM is not high fidelity, it's satisfactory for car use and the MP3 format. However, some models cannot play music and navigate at the same time.

    * Decide if you want to be able to get live traffic reports and alerts. FM TMC, MSN Direct service, Tele Atlas and Clear Channel have subscription-based live-traffic services. Compatible GPS units use a built-in or external receiver -- or a Bluetooth-compatible phone -- to download this info and incorporate it into routing. Check coverage, however. Each service is only available in a limited, but growing, number of major markets.

    * Make sure the screen size is appropriate for your eyesight and vehicle space. The vast majority of car GPS units have 3.5-inch displays. Some, like the Garmin nuvi 660, have larger displays.

    * Evaluate weight and bulk. If you want to use the unit in two cars or as a portable MP3 player, portability is important. If not, you may still wish to carry the unit to reduce the likelihood of theft.

    * Consider a unit with a large POI database (five million or more). Points of interest range from tourist attractions, hotels and restaurants to gas stations and ATMs.

    * Weigh convenience features. A touchscreen is common. Many units simplify text entry by only allowing you to type letters or names in the database. As you start to type, these units may also give you options to select.