For whatever reason, you might want to keep tabs on exactly where your wife/husand/girlfriend/boyfriend/teenage daughter, etc. have been all night (for their own "safety"). In the past, you had to rely on them to telling you the "truth" about where really were.
Thankfully we can bypass all of this guesswork if they happen to own either an iPhone, BlackBerry or Android device, which all contain GPS chips. These devices are capable of pinpointing and broadcasting exact locations at all times over the air. It's actually very simple process to view a smartphone's location just by configuring a few free apps.
Remember, always consult the owner before you make any changes to their device. And as always, with great power comes great responsibility.
What would Spider-man do?