does anyone know what makes the camera to turn on while we open the slide window?
I removed the battery cover and opened the camera window, then I just put the cover on the back (not attached, just touching a bit) and camera turns on, when I removed the back, the camera went off.
what makes the camera turn on?
if you do not understand what I did, please ask for a video

its a magnet.

and it should be that white square, right?

There is a black magnetic strip on the door slider above the magnet under the stand. When the door is opened, the black strip moves away from the stationary magnet (bringing the white strip accross) telling the phone to open the camera.

EDIT: Since found this to be wrong.

aha, i found the magnet. it is inside a rectangular plastic but I still don't get how it's working as the magnet does not move while we slide the window. the magnet is not a moving part

No, but the black strip on the door is magnetic as well. Like a credit card.

and how does the strip communicate with the device to start the camera since it's not connected anywhere on the device?

Good point. Looking inside the back cover, I'm not sure it is the magnet now you know. Look on the inside of the door and then the back of the phone where the sliding strip should be with the door on. It looks like some sort of sensor, that senses the strip moving from black to white (dark to light) It looks like that is how it works to me now.

try with a white paper, it will work as well

so it might need a magnet and a white strip over the "sensor" to operate the camera