Which device decreases resistance when exposed to increased temperatures?

The correct answer is thermistor, which is a type of resistor whose resistance changes significantly with temperature. When the temperature rises, the resistance of a thermistor decreases, making it an essential component in temperature sensing and control applications. This property allows thermistors to accurately measure temperature changes and respond accordingly in various electronic circuits.

In contrast, a thermocouple is a device used to measure temperature based on the voltage generated when two different metals are joined, but it does not have a variable resistance characteristic related to temperature fluctuations. A controller typically regulates other components based on input, but does not inherently change resistance with temperature. The Bourdon tube functions primarily as a pressure measurement device and does not change its resistance based on temperature changes either. Understanding the properties of these devices highlights why thermistors are specifically suited for applications where temperature variation is monitored and managed effectively.