With the installation of a heating device in the lunch box, which utilizes the heat generated by a chemical reaction between calcined lime and water, customers could eat hot Ekiben only by pulling a string coming out of the box.
生石灰と水の反応熱を使用した加熱装置を組み込み、食べる前に紐を引いて加熱する駅弁を売り出した例がある。