Global Positioning System add-ons for smart phones and PDAs are nothing new. But a GPS clip-on? That's what the super-tiny Garmin Mobile 10 claims to be.

Garmin's Mobile 10 is a compact GPS receiver that transmits location information via Bluetooth to Garmin Mobile XT mapping software that you install on a supported smartphone, PDA, or notebook.

The Garmin Mobile 10's GPS receiver locates your position, which is displayed on the mapping software. The software calculates a route to your desired destination(s). You can receive turn-by-turn directions via voice prompts, delivered using your device's speaker. And you can visually follow your route on the mapping software. Recently, we tested the Garmin Mobile 10 with a Palm Treo 650 and we recommend it - with some caveats.

See also Palm Treo 680 review

Convenient to carry

The Garmin Mobile 10 weighs only around 60g and measures 18x42x77mm. It's so small you can take it anywhere. You could also lose it anywhere, but c'est la vie.

The aforementioned clip, which is removable, is a nice touch. You can clip the Garmin Mobile 10 on to your belt and receive directions while walking. Or you could clip the GPS to your car's sun visor while you're driving.

Either way, the Garmin Mobile 10 is delightfully easy to take with you. And because it works with a device we already carry everywhere - my Treo 650 - the Garmin Mobile 10 is the most convenient portable GPS receiver we've seen. There's no extra bulk.

Generally good directions

We tested the Garmin Mobile 10 in San Francisco over several weeks. In most cases, the directions we received were good, but not always the most practical.

For example, in a San Francisco neighborhood we avoid using 24th Street, as it is often congested with mobile-phone-talking pedestrians dawdling on their way to digressing, double-parked delivery trucks, surly teenagers on skateboards, and the occasional Segway. But in many cases, the Garmin Mobile 10 directions had me going by way of 24th Street. Local knowledge still counts for something!