https://www.digikey.com/en/products/detail/soldered-electronics/333104/21720385

There's been a lot of talk about fires & exploding houses. When nature calls, it would be nice to know when methane levels in the room are hitting dangerous levels.  It would also allow the level of CH4 produced by different foods to be quantified.

These sensors need 24 hours to preheat & burn 750 mW.  They're no good for portable applications in a vehicle. 

Testing it would entail eating cheese, beans, whey, biscuts.  Lions are guaranteed to produce methane from cheese.

The trick is it would have to be on the ceiling.  It requires a fiddly calibration.