Heated volatile dispensing device with use-up indicator

摘要

Heated volatile dispensers are disclosed that are provided with automated use-up indicators. The indicators are associated with a porous substrate. A migrateable dye is covered by meltable material adjacent the substrate. Heating of a substrate such as a slab impregnated with an insect repellent both causes the insect repellent to dispense and melts the covering. The dye then migrates to a visible surface of the substrate to indicate a degree of use. The extent of migration, and the patterns formed on the visible surface by the migrating dye, indicate the extent to which the volatile air treatment chemical has been dispensed.