The DHT11 is a basic, 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.

Technical Details:

    -Low cost
    -3 to 5V power and I/O
    -2.5mA max current use during conversion (while requesting data)
    -Good for 20-80% humidity readings with 5% accuracy
    -Good for 0-50°C temperature readings ±2°C accuracy
    -No more than 1 Hz sampling rate (once every second)
    -Body size 15.5mm x 12mm x 5.5mm
    -4 pins with 0.1" spacing