What devices is made of two different metals and produces a voltage when the metals are exposed to heat?

The device you’re referring to is a thermocouple. It consists of two different metals joined at one end, and when this junction is exposed to heat, it generates a voltage due to the Seebeck effect. This voltage can then be measured and used to determine the temperature difference between the hot junction and the other ends of the metals. Thermocouples are widely used in temperature sensing applications.