SparkFun Temperature Sensor Waterproof DS18B20

This sealed digital temperature probe lets you precisely measure temperatures in wet environments with a simple 1-Wire interface. The DS18B20 provides 9 to 12-bit (configurable) temperature readings over a 1-Wire interface, so that only one wire (and ground) needs to be connected from a central microprocessor. Dimensions: Probe is 7mm in diameter and roughly 26mm long. Overall length (including wire) is 6 feet.