A basal body temperature thermometer is a specialized device used to measure a person's basal body temperature (BBT), which is the lowest body temperature during rest. It is often used by individuals tracking their menstrual cycle or fertility, as slight changes in BBT can indicate ovulation. These thermometers are typically more sensitive than regular thermometers, allowing for precise readings to the tenth of a degree. To use a basal body temperature thermometer, it is recommended to take the temperature first thing in the morning, before any activity. Users should record their temperature daily to identify patterns over time. This information can help in understanding reproductive health and planning for conception or contraception.