Gas detectors are categorized by the gases they detect: flammable gas detectors, toxic gas detectors, and multifunctional gas detectors. These detectors utilize different sensors to detect various gases, with multifunctional detectors capable of detecting both flammable and toxic gases simultaneously. By application environment, they are divided into industrial gas detectors and residential gas alarms. In terms of their form, there are fixed gas detectors and portable gas detection instruments.