Whistle 3 comes with an attachment piece to secure the device directly onto your pet’s existing collar or harness (up to 1’’ wide). It's made of super strong rubber and is designed so that you can still use whichever collar you choose.
To secure the attachment to your pet's collar, lay the plastic mount flat on the collar and secure one end of the rubber band to the hooks. Then wrap the rubber band underneath the collar and secure the other end to the hooks on the opposite side of the mount.
The Whistle 3 fits into the plastic mount and then needs to be twisted in order to lock into place. It should feel secure if you tug lightly on the device.
When you want to remove the tracker, just push the side pin & rotate. This makes it extra secure when on your pet but super easy to remove when the device needs to be charged.
Below is quick video showing you how:
Here's a photo of the collar attachment:
Here's a photo of the attachment on a 1" collar:
Hope that helps :)