The Angel Watch works paired with an app called Angel Watch.
The watch is 'paired' to the parent's smartphone using an auto-generated QR code found in the watch's 'QR Code' app once the provided SIM card has been activated and inserted, or WIFI has been connected to the watch.
For your security, once the app is successfully paired the first time, any future attempts to connect to the watch will require the permission of the original app account holder- the Administrator. With connections having the ability to track and monitor your child, this is designed to avoid anyone, other than those you expressly allow, to connect to your child's watch.
If another SIM card is ever inserted, the watch will factory restore itself to remove any personal data, a new code will be generated and the (now wiped) watch will need to be re-registered.
All communication is encrypted and none of your data is ever shared.
To prevent unsolicited calls to your child, unknown incoming calls can also be blocked.