This has been freaking me out recently.
It's a house that has two security cameras (TP-Link Tapo), and they are connected through Wifi to the Wifi router installed in the attic. Their local network IPs are like 192.168.x.x.
I can watch them on my Pixel phone using the Tapo camera app. I don't have any subscription, not paying or anything like that.
So as long the phone is connected to the same Wifi router, I should be able to see them and I do.
But the weird thing is that if I disable Wifi on the phone, and use mobile data, I can still watch the cameras! The IP assigned by the mobile carrier is different than the IP assigned by the ISP to the Wifi router.
How is this possible? The only explanation that comes in my mind is that the phone is somehow secretly connecting to the Wifi too, but this would be like huge privacy breach (from Google) because it's connecting without your consent.