What do a DC drug dealer and a TV show host have in common? The ease at which they both can be tracked by GPS devices without their knowledge. Through a combination of Web technologies and cheaper, more ubiquitous devices, we are now witnessing what could be the golden era of geo-stalking. It is both thrilling and scary at the same time.

Last week, a man arrested for drug possession was set free in DC because the police put a GPS on his car to track his movements. The courts ruled that without a search warrant and without the person’s knowledge that he was being tracked, the arrest couldn’t stand.

Then there was the case of the host of the TV show Mythbusters who was tracked by virtue of information that he posted of a photo of his car. Because he took the photo in front of his house, and because the photo contained geo-tagging information, an enterprising reporter could piece together where the host lived, and bring up an actual picture of the host’s home on Google Maps.

Certainly, having a GPS inside your phone is convenient. No longer can men claim that they know where they are going when their wives can pull up a screen and give them turn-by-turn directions. Another click, and you can find the nearest drugstore or burger joint when in a strange town, or even a not-so-strange one. It amazes me how far we have come and how much and who you can track these days.

Earlier this year, I wrote about location-aware services like Foursquare and Loopt that are used for social networking purposes. But there are a couple of other services that I have been looking at since then that I want to mention.

I have been trying out an iPhone app called Life360 that can be used to connect with family members. You load it up on your phone and connect to your other family members. If you are running iOS v3, as long as you bring up the app to update your position it will let everyone else know where you are. This is its biggest weakness, because you need to bring up the app so your location can be tagged. (It will run in the background on iOS v4 phones, but everyone of your connections then needs to upgrade their phone accordingly.) It also disturbingly posts locations of known nearby sex offenders.

And if you have purchased a Garmin GPS, there is a site that works with these devices called Connect. Your GPS is set up by default to transmit your movements, and the Connect can be used to assemble a map of your regular workout routines if you jog or bike with the device on your person. The trouble is that you can quickly find others movements as well. I found several organized bike rides in my neighborhood, along with someone named Hannah’s running schedule, and lots more.

The iPhone’s default geo-privacy setting is “ask upon first use.” This means that when you run a new app for the first time, it asks you for permission when it wants to access your position. That might not be granular enough, and while it is essential for apps such as Foursquare, I am not so sanguine about publishing any of my photos with the geotags. There is a way to reset this setting, and the aptly named site icanstalku.com will show you how to do this for both iPhone and Androids.

And for the Garmin devices, you should change the privacy settings if this bothers you.

Expect a lot more geo-stalking to happen in the near future. And while it is amazing what you can do with a GPS these days, part of me longs for those bygone days when all you could do with cell phones was dial 10 digits.