An apparatus for the removal of nitrous oxide in a gas stream containing nitrous oxide which is derived from exhalation air and present in the gas stream in a concentration supporting exothermic decomposition of nitrous oxide. The finger voltage sensor can also include a beeper instead of a warning light and a base finger ring that includes a hook and loop fastener that is releasably attached to a user’s finger. The composite dielectric sheet contains a polyvinyl acetal resin; a high-dielectric constant filler, surface-treated with a coupling agent, dispersed in the polyvinyl acetal resin; and a crosslinking agent having two or more functional groups reactable with the polyvinyl acetal resin and the surface-treated high-dielectric constant filler. A noise adaptation rate modifies estimates of noise components based on differences between the signal to the estimated noise and signal variability.