A detector has a thermoelectric sensor and a reactive layer. The thermoelectric sensor is configured to sense heat and to provide an electrical signal based on the sensed heat. The reactive layer is coupled to the thermoelectric sensor and is reactive with an airborne chemical or airborne biological agent of interest. The reaction is exothermic or endothermic. When the airborne agent of interest reacts with the reactive layer, the reaction is detected by the thermoelectric sensor. The electrical signal provides an indication based on the reaction.