Detectors for carbon monoxide are installed in many buildings. They can be standalone or hooked up to alarm systems.
For various hazardous gases there is a sensor made specifically
to detect it.
Smoke detectors are not exactly the same as olfactory sensors. There are optical sensing type, and radioactivity sensing smoke detectors.
Municipalities have different policies about when to send out a fire truck. Some do not rely on an alarm but require a human to call in and confirm a fire.