prior art air treatment device generally 10 it has a housing 12 that contains a heater not shown powered by contact prongs 14 the heater heats an impregnated substrate not shown to drive an air treatment chemical e g an insect repellent or fragrance out radial sides of the housing mounted at the front of the device is a table 18 that can be snapped onto a front wall 20 of the structure that device had a compact indicator unit 100 removably positioned in a recess of the table 18 the unit 100 had a cup shaped storage well 102 for holding a volatile indicator chemical 104 in a cavity defined by the well a permeable multilayer membrane 106 encloses the well 102 by u201c permeable u201d it is meant that a gas phase of the volatile indicator chemical 104 can pass through the membrane 106 even though if in a solid or gel form e g during storage it cannot on top of membrane 106 is positioned a peel off essentially impermeable multilayer membrane 108 this positioning is via a heat seal 110 or other conventional adhesive bond by tugging at a tab portion 112 of membrane 108 that membrane 108 can be pulled off membrane 106 notwithstanding seal 110.