I should have updated this post, the unit from the first post was unpredictable so I returned it to Amazon. I purchased another one which works well and it is almost as small.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
I tested the unit with chocked flame from a small alcohol burner (very yellow flame) and got the unit to sound the alarm, time will tell if this unit will last.