NPG VPS is a smart home app. If you want to use it, you need an our companys smart doorbell, and add it to your apps doorbell table.
When you have set up our companys smart doorbell, you can see who is in front of it in your iPhone/iPad, and you can receive call request where ever you are! The doorbell has alert system, if someone stands or hovers in front of the doorbell, you can receive alarms.