About: 1-Wire Digital Thermometer

Model: Thermometer DS18S20
Purpose: Measures temperature.
Purchased from: www.hobby-boards.com
Details:
Measures temperatures from -55C to +125C (-67F to 257F)
0.5C accuracy from -10C to +85C
9-bit thermometer resolution
 
You are probably saying that it looks like a transistor, true, but it's not.
The two outer legs are connected to ground and the centre pin is the DQ pin or the 1-wire Data line.
 
 
Maxim 1-Wire Temperature Sensor DS18S20 mounted inside a DSE RJ-45 Network cable joiner.
 

Complete inside case.

 

 
Solar Hot Water Sensor mounted on the side of the tank. It is stuck on with a two part glue which has good thermal qualities.
The Sensor has since had an extra layer of silicone sealant to give it extra strength and stop the heat escaping though the sensor.

Solar Hot Water Temp Sensor