Monitor temperature of different rooms

How can I read and monitor the temperature of different rooms or even refrigerators? Do I need 3rd party sensors? How do I pair hem with central unit? Can they interact wireless? Could you please give me some clues what parts do I need and a basic plan or some similar project? Thank you!

Hi, Here's an example monitoring 2 rooms and outdoors, showing temperatures on the web:

Thank you for suggestion! Very detailed information. Any suggestion with wireless sensors that send the measurings to a server and from there to a webserver? Thank you!

You can establish a network using esp8266 WiFi modules, rather than Arduinos per se. These have their own intelligence and may be programmed with the Arduino IDE. They can be had for as little as about $3.

I used 1 nodemcu with 1 DS18B20 and another nodemcu with 3 DS18B20 and all data is sent to

Thank you for help!