Whistle is a Fitbit for your four-legged friends. Attach it to your dog’s collar and pair it with the app. You can set goals (like an hour of exercise a day), track her diet, set up medication reminders, and view her activity by the hour, day, week, or month. Install the app on friends’ phones, and Whistle will keep a log of how long they play with her — a sneaky way to tell if your dog walker is lying down on the job. A GPS-enabled version that tracks your hound’s location is due out in spring.