Product review (5 stars): This is a fire safety item, most helpful for preventing fires in the kitchen.
In some ways, this item is a simple concept.  If a pot is left too long on a heated burner, the heat rising from the forgotten hot pot will activate the Firestop can hanging from the  stovetop hood.  Also simple is the installation of the Firestop.  They come in pairs, one for each side of the stovetop.  They attach to the underside of the hood by way of a magnet.  This item provides a safety back-up for the potentially forgetful cook.  But, having such a back-up is so much better than having a full-on kitchen fire.  The Firestop, when activated by the rising heat, will put out the over-heated, burning/smoldering pot.  Fortunately, I have not had a situation which ended up with the Firestop releasing their fire retard contents.  But, I feel better knowing that they are in place & ready to stop a stovetop burn from becoming a kitchen fire.  And, simple concepts can sometimes be the most effective solutions.