There is a huge variety of sensors that do different things. Here are just a few sensors.
A temperature and humidity sensor, it measures the temperature, and humidity.
There is a smoke and gas sensor that measures the amount of smoke and gases.
A pressure sensor that is used to measure pressure in liquids and gases.
Hydrogen Sulfide sensor, which usually comes from the chemical reactions of a landfill.
Air Quality sensor monitors the surrounding area of any air pollution.