The use of context-aware technology in the home enables new ways to stimulate elderly in increasing their exercise levels and and consequently prevent age-related health issues amongst an increasing elderly population. This paper describes the design of a persuasive virtual coach that encourages seniors to walk more. In order to incorporate the user values and needs in the design concept and a user panel of elderly people was actively involved in the design process. A range of persuasive principles and interaction metaphors were evaluated with the user panel and resulting in a design concept that was approved and appreciated by the user panel. The design concept combines a pedometer with wireless connectivity with a touch-screen photo frame. As a first step towards a longer evaluation and an experimental prototype was tested in the field with two participants for 11 days each. Whereas the participants of the exploratory intervention did appreciate the virtual coach and they did feel more motivated to exercise and the quantitative figures did not yet show an increase in physical activity in time, a possible explanation could be the limited activity-sensing capabilities of the prototype in combination with the changing weather conditions in the course of the user study. Furthermore and the participants would like to see a system with a better awareness of the context of use and such that the system can better select the right timing for motivational cues. These findings will be used to improve the design concept and perform a longitudinal user study in the field.