DHT11 Temperature and Humidity Sensor
The DHT11 Digital Temperature And Humidity Sensor is a basic, ultra low-cost digital temperature and humidity sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air and spits out a digital signal on the data pin (no analog input pins needed).
Its fairly simple to use, but requires careful timing to grab data. The only real downside of this sensor is you can only get new data from it once every 2 seconds, so in your code please use sensor reading interval at 2 seconds or more. Compared to the DHT22, this sensor is less precise, less accurate and works in a smaller range of temperature/humidity.
But despite its disadvantages over DHT22, it is smaller and less expensive sensor for temperature and humidity measurement.

Note:
This package does not include Arduino board, you have to buy it separately.

Features:
-Low power consumption.
-Relative humidity and temperature measurement
-All calibration, digital output
-Excellent long-term stability
-No additional components
-Long distance signal transmission
-Ultra-low power
-4-pin package
-Completely interchangeable