Not so many years ago, if you wanted to record a set of changing data over a given time period, you would need to use a chart recorder. These are mechanical devices that work either with or without electrical power. Although these are still sometimes the best type of device for the job, they have been largely replaced by data logger devices.

A data logger is an electronic device that can either have its own built-in sensors, or that can retrieve data from external sensors. In general, they're small, battery-powered, and contain a microprocessor. They can be stand-alone devices, either with their own keyboards and displays, or that would hold data in memory for later retrieval via a normal computer. On computers, data may be either displayed by a proprietary program, or by Excel graph or spreadsheet. Newer models can also have wireless capabilities, enabling them to send a constant stream of data back to a base station.

Search on the web, and you'll see a wide range of data logger. Prices range from the inexpensive, to thousands of dollars. There are lots of vendors, selling devices for almost any type of data that can be measured.

Vendors with prominent web-front stores sell a large range of logging devices. You'll find devices for use by electricians, network technicians, weather researchers, home owners, etc. It seems that there's something there for almost anyone.

Homeowners may be interested in purchasing an energy audit or monitoring device. Several types are available, including one that can measure the power draw of an electrical appliance, and automatically calculate its annual energy cost. There's also a monitoring kit that enables you to constantly monitor room temperature throughout the house.

Logging devices for industrial or small business use include monitors for HVAC, greenhouses, refrigeration units, or air quality. Air quality monitors can keep a constant check on levels of atmospheric carbon dioxide, carbon monoxide, or other gasses. Use these in closed spaces, where there may be a danger that these gasses may accumulate.

Taxi cab companies, trucking companies, or any other fleet operator, could benefit from using automotive data loggers. These small devices, when connected to a vehicle's OBD-II port, can track many different data. They can monitor fuel economy, engine performance, and how the driver is operating the vehicle. Devices with wireless capabilities can allow an operator at a base station to view real-time data as a vehicle is being driven. An auto mechanic can use OBD-II devices to help diagnose engine problems.

Weather researchers can choose from a number of different monitoring solutions. You can purchase loggers for specific weather data, such as humidity, temperature, wind, rainfall, or soil moisture. Complete weather monitoring stations allow monitoring many different types of weather data.

Operators of mines or grain elevators, where combustible gas or dust may be a problem, would want to use an "intrinsically safe" monitoring device. These devices are guaranteed not to produce sparks that could cause an explosion.

When shopping for a monitoring solution, be aware of what's included in your purchase. Oftentimes, the price of the data logger device doesn't include the required sensors. So, you'll need to purchase them separately.