Internet-enabled motion sensor?

Question

Iron

There are several rooms (garages) in the city, for each of them it is necessary to collect statistics on when there is movement in them during the day, and when they are not. Identifiers on the door are not an option.
All information must be collected and sent via the Internet to a central server. There is no internet in the rooms.
Question: how to implement it?
Apparently, you will have to use the mobile Internet as the Internet, but how then to connect the sensor to the phone?
Or is it difficult to use sensors and instead of a sensor it is easier to use video cameras and request a picture from an object by ip?
Something like this would be cxem.net/review/review9.php only not in security mode but collecting statistics

Answer 1

An excellent solution would be: any motion sensor + raspberry (Raspberry Pi) + usb gsm whistle.

Answer 2

you can use any cheap Chinese mobile phone with android and use its camera to determine the movement. It will most likely be cheaper than a raspberry with a motion sensor and a whistle. But it will work worse in the dark, motion sensors are usually infrared, but there is no mobile camera