If you have ever used a disposable heat pack to keep warm during the winter cold, you have seen how it suddenly becomes warm after opening the bag and shaking it. This is because of the iron-based chemical substance used: oxygen molecules adhere to its individual grains and generate heat in the process.

A substance known as titanium is used in the oxygen detector tube. Besides changing colour when the oxygen molecules adhere to the titanium grains, heat is also given off (similar to the disposable heat pack).