In the previous sessions, a general overview of sensor networks was given. In this session,I will focus on a system for monitoring human activities that can be attached to the human body,similar to adhesive plasters, as an example of an application of a sensor network. Because thissystem consists of various sensors, a microcontroller, a RF module, and a power source, the systemcan be regarded as a typical example of a sensor network. The specific requirements for this systemcompared to other sensor networks consider their weight, size, and shape. When the system isattached to the human body, the weight, size, and shape of the entire system greatly affects thecomfort felt by users. To improve the comfort for users (that is, reduce the discomfort experiencedwhen the users wear the system), we have made an effort to not only reduce the size, thickness, andweight of the entire system as much as possible but also to use multiple small printed circuit boards(PCBs), instead of using one large PCB, mounted on a flexible substrate.