An autovent is a device for maintaining a greenhouse or conservatory within a range of temperatures.
The force to open the vent is provided a number of ways, the most common being through thermal expansion and by electric motors.
This approach is cheap, reliable and passive (requires no external energy).
The vents can form part of a more complex climate control system for controlling humidity, fresh air rate and temperature.
The most sophisticated systems use a dedicated computer to control watering, cooling (usually evaporative cooling), heating, lighting, CO2 injection fertilization and air flow.