Sapnaben Chunara spends most of the day outdoors because it is even hotter in her tin-roofed house in Vanzara Vas, a low-income neighborhood on the outskirts of the Western Indian city of Ahmedabad. Indoor temperatures can be hotter, especially when outside temperatures climb above 40 degrees Celsius (104 F). That was once rare but now happens regularly. And this year, high heat started three weeks earlier than in previous years, touching 43 degrees Celsius (109.40 F) in early April. Chunara is one of 204 residents of Vanzara Vas given wristwatch-style health monitors as part of a year-long study to find out how heat affects vulnerable communities around the world.