When you install the app on your child 's device, it is a target device and the app will know the telephone number as well as device id (IMEI or other system information).
After that, you can hide the app by making a call (dial) with the access code, and then you can start to track all activities remotely. For example, you can view the log data with the user control panel site, and adjust settings remotely.
However, when the target device has no internet connection (that means it is offline), you can not adjust remotely with the user control panel. In this case, you must use SMS commands to control the target device.
In order to use SMS command, you must use the predefined telephone number that you use to send (compose) content to the target device.
The predefined number: it is a "monitor number". Normally it is your telephone number (also other names are admin number, server number) which used to send to the target number (client number).
1) You can enter with any format. All below are the same:
+1 (214) 612 - 1234 or
2) This 'monitor number' is used to send an SMS command to the target device to adjust the settings remotely, also it is used to make a spy call (silent call) to target device without knowledge of the target users.