If you have a Grove shield from SeeedStudio, we can use the Grove flame sensor to detect a fire. Technically, this sensor uses the YG1006 sensor with high photosensitivity. This sensor is easy to use on Arduino and Raspberry Pi. If you are interested, you can visit the website to obtain further information: https://www.seeedstudio.com/Grove-Flame-Sensor-p-1450.html. You can see the Grove flame sensor here: