Health management is fundamental to enabling elderly people to ‘age in place’ in their homes, and health care services can help elderly people to manage their health. The number of elderly people who require such care services is increasing rapidly, causing a parallel rise in the need for expert care providers. One of the solutions to this demand for expert care is an automatic health care system that may be integrated into a residence, but installing and operating such systems can be prohibitively expensive. To solve this issue, a cost-effective activity monitoring based health care system is proposed in this study. The system uses the infrastructure of a smart grid and a home network system in order to reduce the costs of installation and operation.