For Dr. Jeff Weber, a veterinarian at the Century Group in Los Angeles, there has always been a gap between what he can see in his office and what’s really going on with a dog. “The thing is, animals act very differently behind closed doors, when they are alone, than they do around people, especially their owners.” Often, Weber says, an owner will notice a dog is limping. But when he examines the animal at his office, it walks normally. “All the adrenaline and the desire to show off overcome the injury.” Whistle, a new gadget that tracks your dog’s activity, hopes to solve that problem. It’s a small circular device about the size of a watch face that attaches to the dog’s collar. It uses an accelerometer to tell if the dog is walking, playing or sleeping. Whistle sells for $99.95, including a companion app and free web service. The unit relies on Bluetooth for the mobile app and Wi-Fi for remote monitoring.