This concept is used by traditional alarm services and means that the perimeter of your home is secured, meaning doors and windows. This means the alarm will detect opening of windows and doors, and this is typically turned on when going to sleep and you don't want to trigger the alarm when moving around inside the estate. Another reason to just secure your estate doors/windows and not the interior could be that you have pets that might trigger the photo sensors or body heat sensors monitoring your interior. Alarmhandler not supports "Home ON" for both SMS alarms and IP cameras. For SMS alarms, the app will send the control code to your alarm to enable perimeter sensors. For IP cameras, the cameras that you've marked as "perimeter" under settings for the camera are enabled when you tap "Home ON".