Background Technologies such as social alarm systems contain expectations about how they should be integrated and used in practice. These expectations, also called technology scripts, usually fail to consider all the complexity in care practice. Shifting the focus from technology scripts to care practice, this paper examines how a social alarm system is used in assistant nurses' care practices in nursing homes. Methods The paper draws on observations of assistant nurses' daily tasks (32 h) and semi-structured interviews with assistant nurses (n = 12) in two Swedish nursing homes. The observation data were used to understand the care contexts and assistant nurses' technology-mediated care practices, while interviews were used to deeply understand assistant nurses' perceptions of the system, their care practices, and which aspects they considered during the provision of care. Findings We show the complexities involved in integrating a social alarm system into care practices based on assistant nurses' situational and personal interpretations of both technology scripts and quality of care. The technology-mediated care practices consist of receiving alarms from residents, checking alarms via alarm phones, responding to alarms via alarm phones, checking specific residents' situations in person, documenting all finished alarms, and documenting some finished alarms. In these practices, the assistant nurses defined technology scripts according to their expected requirements and outcomes, and meanwhile considered the quality of care by evaluating the priority of practical, moral or relational care in the situations at hand. Through further negotiations with the defined scripts and the considered quality of care, the assistant nurses decided on the final way of following (or not following) specific scripts in practice. Conclusion Results from our study portray the complexity of technology in care practices. The findings contribute to increased understanding of technology-mediated care practices in nursing homes, and research on technology scripts in institutional settings.