BACKGROUND: Policy makers and care providers see assistive technology and telecare as potential products to support people with dementia to live independently in their homes and communities. Previous research rarely examined how people with dementia and their caregivers actually use such technology. The study examined how and why people living with dementia and their caregivers used assistive technology and telecare in their own homes. METHODS: This study used an ethnographic design embedded within the NIHR-funded Assistive Technology and Telecare to maintain Independent Living At home for people with dementia (ATTILA) randomised controlled trial. We collected 208 h of observational data on situated practices of ten people with dementia and their ten caregivers. We used this data to construct extended cases to explain how technologies supported people with dementia in home and community settings. RESULTS: We identified three themes: placing technology in care, which illustrates how people with dementia and caregivers 'fit' technology into their homes and routines; replacing care with technology, which shows how caregivers replaced normal care practices with ones mediated through technologies; and technology displacing care and everyday life, which highlights how technologies disrupted the everyday lives of people with dementia. DISCUSSION: This study exemplifies unintended and unanticipated consequences for assistive technology and telecare uptake in 'real world' community-based dementia care. It underlines the need to identify and map the context of technological provision over time within the changing lives of people with dementia and their caregivers.