The purpose of a thermostat is to regulate temperature by controlling heating or cooling systems within a building or vehicle. Thermostats detect the ambient temperature and maintain it within a set range, providing comfort and energy efficiency. When the temperature rises above or drops below a specified point, the thermostat prompts the HVAC system to turn on or off as needed. Modern thermostats can be programmable or smart, allowing users to set schedules or control them remotely, further optimizing energy consumption while ensuring a comfortable environment.