How to set up Shelly Door and Window Sensor

What is Shelly Door/Window 2?
The lightning-fast smart, door and window sensor. Integrated temperature and LUX sensor.
Shelly Door/Window is designed to detect and report the opening and closing of doors and windows. Its compact design allows it to be easily installed on any door or window, and because it is lightweight, the sensor is nearly invisible.
Features
No HUB is required.
Detects and reports the opening and closing of doors and windows.
Integrated temperature and LUX sensor.
It can be integrated to work with all other Shelly devices.
Compatible with Android, iOS, Amazon Alexa, Google Assistant, and home automation servers using MQTT, CoAP, and REST API.
Easily make your Arduino project live and usable in your automation project.