Thermocouples:
> Contact
In electronics, thermocouples are a widely used type of temperature sensor. They are cheap, interchangeable, have standard connectors and can measure a wide range of temperatures. Thermocouples maker use of the Seebeck effect, discovered in 1822. This is where two dissimilar metal alloys produce an electro-motive force ("voltage") that is nearly proportional to temperature. A thermopile is a group of thermocouples connected in series.
Types of Contact Sensors
Resistance Temperature Detectors or RTDs
Other Contact Sensors:
Filled System Thermometers
Bimetallic Thermometers
Semiconductor Temperature Sensors