As stated in the "Connecting via Bluetooth" subsection in the "Data Storage and Retrieval" section of the HS2 Instruction Manual: “The first time the HydroSense II unit is used with a new computer, the computer and HydroSense II must be ‘paired’ before a connection can be made. The pairing code is ‘1234.’” For more information, see the "Connect to a Device" subsection of the "Quickstart" section of the HydroSense II Support Software User Guide.