The technology provides an external device for estimating a core body temperature of a human subject, and a system for use in a local area, such as a school, hospital, workplace, and the like. The wrist monitor device includes a casing sized and shaped to fit onto a wrist of a human subject. The casing has a first face and a second face. In addition there is a cavity in the casing that houses a heat trap. The heat trap has an opening oriented to receive incoming thermal energy and a shell of a thermal-insulation material that has an inner thermal energy-reflective surface. Detected temperature data is compiled in a database and used to estimate whether an identified individual has a core body temperature indicative of a fever. There is also provided a system for identifying persons and screening the persons for a febrile condition. The system may include the steps of: identifying a person using data input by the individual or detected from indicia of the person and previously stored data about the person detecting a temperature condition of the person determining whether the person has a febrile condition using the detected temperature condition and previously stored temperature data of the person and taking action to restrict ingress, deny ingress or allow ingress, based on the determined febrile condition of the person requiring ingress.
