The scoop: GPS Snitch, by BlackLine GPS, about $400 (plus service fees).

What it is: GPS Snitch is a 4-inch portable device with a GPS radio and wide-area wireless network connection (it connects via GSM) that lets it communicate back to BlackLine servers. In addition to the GPS and GSM radio, the device includes a motion sensor that sends alerts to the user (via mobile phone text message or e-mail) when motion is detected, making it a useful theft-prevention device (the device doesn’t include an audible alarm, so if the device is hidden in a car the thief won’t necessarily know it’s there).

Click to see: GPS Snitch

Location data can be accessed via the Web, where users can track on demand, or set up continuous tracking, in which the GPS Snitch is pinged every 5 seconds or so to determine a location (useful for cars that are moving). For each request, the user is charged a credit, so users need to buy either pay-as-you-go TrackPacks that include a number of credits (varying from 5 cents to 10 cents per credit), or buy a monthly or annual plan that provides a bundle of credits.

Why it’s cool: The GPS Snitch name implies spying or other nefarious purposes, and if that’s what you want to use it for (checking up on your spouse or driving teenagers), then feel free. But the device also can be used in nonmalicious ways, such as a business that wants to track where its vehicles are at any given time, or people who want to make sure their elderly parents are safe.

The tracking Web site was easy to use, with locations placed on a Google Maps interface. The location data also could be loaded into Google Earth, providing satellite images of the device’s location. When I tested GPS Snitch (by telling my wife that I was placing the device in her car), I was able to watch as she went to the grocery store and run other errands. When she came home and I asked her about the store, she told me she had forgotten that I had placed the device, and was a little shocked (imagine if I hadn’t told her that I had placed the device in the car).

Some caveats: Continuous tracking eats up credits quickly, especially if you’re asking for a location every 5 seconds (you can set up a schedule if you want to track the device over a longer period, but this still costs credits). On-demand tracking is useful to find out where the device is at that moment, but in order to see where the device is heading, continuous tracking must be used, and that can get costly. Also, I would have liked the ability to see a route that the device took on a map, other than a series of dots on the map for each tracking request.