Recent proposals for reform in England have presented widely available “smart” mainstream digital devices as a means to address some of the challenges facing adult social care and as alternatives to unsustainable analogue “telecare” systems. Drawing on 40 interviews with experts from local authorities, the care and technology sectors, and people with lived experience of social care services, we explored how mainstream technologies are being used in practice in England and critically examined their potential to contribute to policy priorities of wellbeing and sustainability. Across all expert groups interviewed, examples were cited in which the use of mainstream devices supported the economic sustainability of adult social care and/or enhanced aspects of wellbeing, moving the role of technology in care beyond monitoring and managing risks. However, when viewed through a three-dimensional conceptual lens that includes material, relational and subjective wellbeing, the use of smart devices in practice also created tensions and trade-offs between the dimensions, with implications for sustainability. The various ways mainstream devices are being used in adult social care also raised complexities related to risks, responsibilities, and inequalities and required “wraparound services”, tempering their ability to deliver cost savings. To address these issues, we suggest a person-centred approach to technology across local authorities, with investment in wraparound services and to mediate inequalities associated with the “digital divide”.