Your sensor state tells you if your sensor is in an alert state or not. If it is in an alert state it will have a red dot under state in 'Sensor View' and if not in an alert state it will appear as a green dot instead.

In order for a sensor's state to change to red from green it will need to have met all the criteria of an alert to be triggered. Once the alert is triggered the sensor will go into it's alert state and will stay that way until the sensor no longer meets the alert conditions. That is the only way that the state can return to green.