For both indoor and outdoor pools, a chlorine detector is required to ensure the health and safety of bathers and employees. An over-accumulation of chlorine (Cl2) in the air combined with failure of the ventilation system of an indoor public pool can cause irritation of the mucous membranes, chest tightness and even death. Even if the chlorine is non-flammable and non-explosive, chlorine is an important danger to be monitored not only for swimmers, but also for personnel directly in contact with this disinfectant.