A data logger is an electronic device that records data over time or in relation to a changing location. For this task built in instruments or sensors or/and external instruments and sensors may be utilized. These devices address a wide range of applications, both for general- and special-purpose situations. Special-purpose data loggers are available for temperature and humidity, voltage, thermocouple, and event applications to name just a few. Loggers range from inexpensive single channel devices to complex and fully autonomous multi-channel stations.