What is a viewer app?

The app you installed on the target device, it called the target app.

For example, if you want to track your son's device, which is a Samsung device (Android version 9.x), you must install the app on it.

And then, after installing and configuring, you will access the Cpanel website with your PC or your table or any device with a browser (for example, Chrome, Firefox). It is a Cpanel website.

However, you can download and install one app on YOUR phone/device to view the tracked data of your son. It is called the viewer app.  Of course, this is an option. Almost all parents use the Cpanel website to view the data logs sent from the target device.  No need to install another app to view the data.