One Wire Waterproof Temperature Sensor DS18B20
This is a highly accurate and reliable temperature sensor for the Raspberry Pi. The DS18B20 digital thermometer provides 9-bit to 12-bit Celsius temperature measurements and has an alarm function with nonvolatile user-programmable upper and lower trigger points. The DS18B20 communicates over a 1-Wire bus that by definition requires only one data line (and ground) for communication with a central microprocessor. It has an operating temperature range of -55°C to +125°C and is accurate to ±0.5°C over the range of -10°C to +85°C.
In addition, the DS18B20 can derive power directly from the data line ("parasite power"), eliminating the need for an external power supply. (But this version no support the parasite power, please note that).