The sensor used in this video is an analog temperature sensor known as a thermistor and it is part of a 37-sensors kit. It can sense small changes in temperature. The output doesn’t give you exact temperature like digital sensors used with Arduino libraries, but it can be used in areas where is important to keep the temperature constant. While testing this sensor output was 500 for room temperature on Serial Monitor. As soon as the sensor is touched, changes in values are noticeable which means it is very sensitive. This sensor has inverted logic: if the temperature is decreasing, the value of output will increase.
the sensor has three leads, GND, VCC, and DATA.
DATA pin should obviously be connected to an analog pin of Arduino. In this case, that was pin A0.
Besides the sensor, this circuit contains two LEDs. One red and one blue. Red LED will be turned on if values are under 450 and a blue LED will be turned on if values are above 550. This is a simulation of monitoring temperature changes. LEDs are connected to digital pins 2 and 3 via 220ohm resistors.