The user interface for a proposed alternative emergency service was conceived and designed for a standard touch-tone telephone. The service would allow a user to activate an automated, pre-recorded message containing information to aid emergency responders. The user must only press a few specified keys on the telephone key-pad, avoiding the need for verbal interaction with a dispatcher. The interface was designed in terms of providing the necessary instructions for activation and considering various input strategies and feedback. Icons, written instructions, and voice feedback were employed in the development of a successful and effective interface between the user and the system. Because the system is expected to attract elderly users and families with young children, the performance and attitudes of these two age groups in regard to a system prototype were examined to determine if the interface was suitable. A two and eight second initial system response time were imposed upon users to determine any effect these delays might have on user response time, error rate, and subjective attitudes. Additionally, a secondary task, designed to increase cognitive loading was employed to determine if the system is usable while the user is engaged in a dual-task environment. The dependent variables used to gauge the effects of the manipulated variables include the objective measures of user response time and error rate and subjective questionnaire responses. The results of the study indicate that the elderly adults and young children were able to activate the system successfully. System response time and cognitive loading had no significant effect on user performance or subjective attitudes. Distinct practice effects were observed. Attitude scales indicated satisfaction with the service and its interface. Finally, a significant effect of age was observed on average user response time, with the elderly activating the system quicker than the children. / Master of Science