It's not just companies that can use location data from mobile phones. You really can try this at home.

For today's smartphones, there are a lot of apps that can help with directions, locate a favorite coffee shop and even find where your friends are.

Ryan Dube works in IT and writes a technology blog for makeuseof.com. In an article about Google's Latitude app, he demonstrated how easy it was to find his friend in Derry.

But Dube, who lives in Maine, warns that if you don't set up an app like that correctly, you could end up broadcasting your location to everyone else, as well.

He's not too worried about adults. But he won't let his own children use smartphones. “You don't want your kids letting the world know where they are all the time,” he said.

Dube said a cellphone is in essence a tracking device. And he said that can be a boon, for example, when police are trying to find a missing child who has a cellphone with him or her.

However, he said, “I don't think many people really realize that if you have a cellphone, your cellphone company or the government or other authorities can find you.

“I think if more people knew that, they might not carry their phones around with them so much.”