A portable end device, such as a bar code scanner, may be equipped with auxiliary interfaces. The auxiliary interfaces may be easily added to the end device as a replaceable cover, such as a replaceable battery door. A signal path conducts signals to and from the replaceable cover. One auxiliary interface is a Bluetooth radio. Data integrity protocols may be selected to guarantee delivery and guarantee no duplicate deliveries. Host pairing algorithms may provide standard or strong pairing with a host computer. Ergonomic interface features allow a user to control and monitor the operation of the end device and the data link with minimal hardware cost and battery life impact. Host software programs provide data routing, automatic reestablishment of the data link, and other functions. The system is adaptable to a wide array of use environments through the selection of timer parameters in the end device.