Abstract: The down hole and above ground data loggers according to the present invention can be used with any sensors or probes. The switching associated with different sensors is accomplished on a circuit board in the data logger using an external device. The data loggers can send data to the external device via hard wire or radio frequency. Sending the data via radio frequency eliminates the need for a user to go out to the field. Thus, the user can obtain real time and historical data without having to go out to the field. In one embodiment, a down hole data logger is disclosed that is capable of being installed or deployed in small openings. In another embodiment, an above ground data logger is disclosed. In both embodiments, the data loggers can record analog sensor data or discrete data. The data loggers of the present invention are easy to use, reliable, accurate, cost efficient, and feature rich.