To safeguard against fire by propane cooking gas or poisoning from carbon monoxide from kerosine oven or diesel heater a gas monitor and alarm is important.
With gas sensors easily available it's rather easy to put together a small gas detector. Using the the MQ type gas sensors and a small microcontroller like Arduino Nano the setup can be quite small, fitting in a smoke detector housing. Software is found on github.
My version employ an Arduino Nano Microcontroller, two MQ gas detectors, one for light hydrocarbons and one that include sensitivity for carbon monoxide, in addition to a high pitch buzzer that should wake us up if there is any of these gases present inside.