First, second and third current generators, and first and second switching devices are provided. The bandage has a hypoallergenic layer with a contact surface, an adhesive on the contact surface, and a dressing attached to the contact surface. In one form the gas detection apparatus forms part of a system for detecting a condition in an environment that includes, a particle detector; a duct system in fluid communication with the environment and the particle detector and an aspirator to draw an air sample flow from the environment to the particle detector. Candidate address data matches from the point level data set are saved when no exact match is determined as existing in the point level data set.