Safety valve / pressure indicator
The pressure cooker's safety valve automatically checks the internal pressure. When the cooker's internal pressure rises, the valve post lifts and the red cap appears from the hole in the handle. When the cooker's internal pressure drops to a safe level, the valve visibly lowers. This lets you know it's safe to open the lid.
For safe operation, the safety valve automatically releases excess pressure. If the lid is not securely locked, the internal pressure will not rise and the safety valve will release the steam pressure. In this case, simply turn off the heat source and lock the lid properly.