A mechanical interface (84) for a PDA (80) allows the PDA to be positioned in an operative relationship relative to an electronic lock or electronic lockbox (82). The mechanical interface allows the PDA to be used as a key (80) to actuate the lock, by transmitting signals from the PDA to the lock. The PDA retains its normal functionality as a general purpose computer, and the interface can also form part of a link between the PDA and a remote computer (88) and/or database (92).