Abstract: A creosote detector for ascertaining a critical amount of creosote buildup on a chimney flue includes a collector probe mounted contiguous to the chimney flue for a buildup of creosote material thereon. An electrical resistance is variously detected corresponding to the deposit level of the creosote across two conductive plates of the collecting probe. A silicon unilateral switch is designed to operably respond to a certain resistance presented thereto causing the silicon unilateral switch to conduct which triggers the alarm circuit including a flag alarm mounted to the exterior of the chimney proper. Thus, the homeowner is warned of a critical creosote buildup within the chimney flue so that preventive maintenance can then be performed.