The Whistle Activity Monitor is 1.5" wide and 0.4" high, and weighs 0.5 ounces. Although the device works on pets of all sizes, in our experience it fits nicely on pets larger than 10 pounds. The device also features an adjustable strap, compatible with all collars and even harnesses.

To get a better sense of how the Whistle Activity Monitor fits on a smaller pet, meet Duke, one of our smaller dogs, sporting the device.

Duke is officially Ben's dog and unofficially Whistle's mascot. He is four years old, greets everyone like they're his long-lost best friend, and loves strutting around San Francisco. Duke appears in your Whistle app as a way to give you a window into Whistle, as well as show the product's features (and introduce some new ones...). Be sure to leave comments for him, too—the guy loves attention.

Note: Click here for more information on how to follow other pets.


To find out if you can use a Whistle GPS on cats or other small pets, click here. To find out if you can use a Tagg GPS Plus on similar pets, click here.