iButtons are designed for the logging of temperature with a range from as low as -40°C to at the most +140°C. Different iButtons are designed for different temperature ranges. Hygrochrons contain an on-board battery and can log temperatures and humidity at regular intervals even when not connected to a computer. Each has the ability to log temperatures all the time or only when the temperature reaches an alarm threshold.
In addition to the functionalities of the Thermochron, the Hygrochron adds humidity sensing to the iButton. The humidity data it stores is relative humidity, it will show humidity changes over time.