The DHT-21 sensor is a technically identical special design of the DHT-22, which is characterized by a much higher accuracy and a larger measuring range, both for temperature and humidity, compared to the smaller DHT-11.
The DHT-21 is also used as room temperature and humidity meter. If it is to be used outdoors, it must be protected from the weather (rain and direct sunlight). If you want to view your sensor data anytime and anywhere on your smartphone, you can do this quickly and easily with an ESP8266 (e.g. NodeMCU or ESP-12), the free available firmware from Sensate, and our Sensate Monitor App, without having to program yourself. In addition, the sensor can be quickly and easily connected to your own smart home with MQTT, or to third-party products via IFTTTT.