If you already have a Whistle Activity Monitor and want to start using a Whistle GPS tracker as well, you need to keep in mind that a single pet cannot have two devices associated with its profile.
If you decide to use both a Whistle Activity Monitor and a Whistle GPS, you will have to set up the Whistle GPS tracker as a new device, with a new pet profile.
Click here for information on setting up Whistle GPS on your Android device. Click here for setting up Whistle GPS on your iOS device. When you reach the steps for creating your pet's profile, make sure you type in a new name for your existing pet.
This will make make sure that you have two profiles, with one device on each. When you want to check the data collected by either device, make sure you select the appropriate pet in the Whistle app.