There are really only a handful of truly useful gadgets for dog lovers. The Tagg Tracker ($100, plus $8/month) is one of them. This GPS collar clip and charger station lets you track not only how much exercise your dog is getting during a given day, but also monitor his precise movements. The subscription service may come with a hefty upfront cost, but you'll get fast and accurate location updates and the piece of mind that comes from knowing exactly where your furry friend is.
Image: Snaptracs, Inc.