Button to heat the steering wheel.
An improved design would have an option to either control the temperature and/or turn it off automatically after 3 minutes. Another option might always activate when entering the car and the temperature is below a set limit.
Optional on a number of vehicles. For example, a 2013 BMW 328i has a heated steering wheel option for $190.
As of 2021, a heated steering wheel is included as standard in all vehicles. For original the Model S, it was added in Dec-2014 as part of the optional cold weather package (which is standard now).