Ionization smoke detectors work by placing a tiny amount of radioactive material in an air chamber, which keeps a small electric current flowing between two electrodes. When smoke particles enter the chamber they attach to the charged air particles and disrupt that current, and the alarm triggers. The idea came about in the late 1930s when Walter Jaeger was trying to build a sensor for poison gas and failed. He noticed that smoke from his cigarette made the current on his meter drop, and subsequent modifications led to the first commercial smoke detectors.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.