The Ozone or the O3 is an anti-bacterial sterilisation unit which automatically kicks in after you turn off the control panel. A standard feature on all steam showers, the O3 comes on automatically after the control panel is turned off. This kills off bacteria which has built up during the steam or showering session. A very faint buzz can be heard with the Ozone working, however, do not be alarmed if you cannot hear it as it is a very high-frequency sound.