Simple idea but hard to display. At top, verticals line is small piece of paraffin separating two copper or brass spring strips of metal on each side of paraffin. Other two single throw switches is the same design with paraffin holding electrical circuit open.
When paraffin melts (125°F. to 165° F.) copper or brass metal clips complete bell circuit - where lamp is - sounding fire alarm. These switches may be added to existing doorbell circuit if bell stays on when circuit is closed.
