A technique of knowledge-based authentication receives information from third parties as to a user’s recent web history including purchase history at an on-line retailer or search engine queries to produce a challenge question to authenticate the user based on that recent web history. The monitoring apparatus includes a flow path 424 having inlets 420, 422 communicating with the inlet 304 and outlet 306 of the ozone injector main water pipe 302. The piston can move within a first housing inner chamber that is in fluid communication with a second housing inner chamber. Furthermore, inside the case member, provided is a hollow portion that is not filled with a sealing resin. The cavity effectively integrates the energy of different wavelengths, so that the combined radiant energy emitted through the aperture includes the radiant energy of the various wavelengths.