Motivation - Develop a portable, mobile information and communication device with specific applications that meet the identified needs of people with mild dementia. Research approach - A qualitative study with a user centred design was applied: Three iterative development cycles of one year each were performed, in which around 15 persons with mild dementia and their carers participated in each cycle of development to attune the functions and form of the cognitive prosthetic to their needs and wishes. A mixed methods approach of qualitative interviews and standardised tools were used for the evaluations that were performed by formulating research questions and assigning appropriate methods for data collection before, during and after the field tests at the end of each development cycle. Findings/Design - The COGKNOW Day Navigator consists of a touch screen, a mobile device, sensors, a home hub and a central server. Several features such as colours and icons, can be adjusted to personal preferences, which was much appreciated by users. The functions to support people in their daily activities were overall appreciated, though there were individual differences in preferences and abilities to use them. Research limitations/Implications - It was recommended to perform an impact study within the target group for a longer period of time when the system is considered stable and to make use of a randomised controlled design in a larger study population. Originality/Value - The research built upon previous evidence of needs of people with mild dementia and the findings are valuable in directing further research and innovation. However, it was found that this technology can be complex to implement in a manner that ensures good quality of service delivery during field tests. Take away message - The work has shown the value of designing an analysis framework for development of assistive technology that gives a strong voice to people with dementia and their carers.