Humidity meters are a useful device to help to ensure that your home or workplace is kept at a reasonable humidity. It is a good idea to monitor the humidity to avoid problems caused by dampness or extreme dry conditions. Here are videos and links a look at how they humidity sensors work and how you can check their accuracy and how they work.
Arduino – Humidity Sensor © GPL3+
The room temperature and humidity will be printed to the serial monitor.
How to Pick the Best Temperature and Humidity Sensor for Your Arduino Project