Background. The quality of life of the person with dementia is often impacted by a loss of autonomy and independence that can arise during dementia progression. Ambient assistive technologies represent a way of enabling independence and facilitating “ageing in place” by supporting the health, lifestyle, and safety of the person with dementia in an unobtrusive manner. We investigated their use in five frequently problematic areas for people with dementia: sleep, daily living activities, physical activity, social interaction, and mood. Methods: This study was part of the EU-FP7 Dem@Care project examining the use of ambient and wearable sensors by people with dementia and their informal caregivers. We used a multiple case-study design with purposive sampling of people with early stage dementia. An individualised sensor “toolbox” and intervention strategy was developed for participants based on a clinical assessment of their needs across the five domains of interest. Sensor data was aggregated over time (up to 18 months) to identify changes in behavioural patterns that could signify improvement, stasis, or the possible deterioration of function. Results: Sleep patterns for all participants remained stable over time, but objective monitoring found high levels of sleep interruptions and recurring ‘problematic’ sleep episodes. It also highlighted the influence of physical activity levels on sleep quality, thus increasing awareness of behaviours that were detrimental to health and well-being. Functional decline was found in some activities of daily living but not in all, and rehabilitation strategies were successful in some but not in all cases. Sensors were generally acceptable to participants providing they functioned accurately, were unobtrusive, and required little or no new learning. Difficulties obtaining informed third-party consent restricted the use of ambient video cameras in the home, as did their potential mis-use as survelliance tools. Conclusions: These results demonstrate the ability of multi-sensor systems to support “ageing in place” by preserving autonomy, promoting independence, and facilitating home-based living for longer. There remains a need for discussion, however, of the ethical challenges that can arise with the use of these technologies in a vulnerable population.