A wristwatch contains communication and memory circuitry and a transmitter. The memory circuit stores a personal identification number of a single user. The communication and memory circuitry is driven by the same battery which powers the timekeeping structure of the watch. A transmitter transmits data from the reader to the wristwatch, placed proximate thereto. The reader has a keypad by which the user can enter a personal identification number, and the watch compares the transmitted number to the user-entered number. If the numbers match, a transaction may occur.