A device for evaporating a volatile air treatment agent from a replaceable refill is described herein, the device comprises: a housing with at least one exit orifice for evaporated air treatment agent to exit the device, receiving means within said housing to releasably receive and secure the refill to the device, electrical heating means within said housing, control means and chimney means within said housing having a lower orifice and an upper orifice to define a first airflow channel therebetween an airborne agent detector means operable to detect airborne agents in the air, wherein said means are provided with at least one aperture to the exterior of the device to permit, in use, air from outside of the device to enter said airborne agent detector means, wherein the refill for use with the device comprises: a reservoir portion for holding a quantity of volatile air treatment agent: and a wick having a proximal end within the reservoir portion substantially adjacent a base of said reservoir portion and having a distal end extending above the reservoir portion and wherein the device is configured such that, in use, the securing means are adapted to hold the refill such that the distal end of the wick is located within the chimney means, characterised in that a second airflow channel is provided between said at least one aperture of the airborne agent detector means and said exit orifice
