They generally are small, battery-powered, portable, and equipped with a microprocessor, internal memory for data storage, and sensors.
While it is common for general-purpose types to be programmable, many remain static machines with only a limited number or no changeable parameters.
Upon activation, data loggers are typically deployed and left unattended to measure and record information for the duration of the monitoring period.
This allows for a comprehensive, accurate picture of the environmental conditions being monitored, such as air temperature and relative humidity.
Data loggers are beginning to serve web pages for current readings, e-mail their alarms, and FTP their daily results into databases or direct to the users.