To better monitor the care receivers, we developed a new motion detection method based on device-free localization (DFL) using Bluetooth. As will be described in detail below, this method utilizes an attenuation of Bluetooth signals. Because the human body is about 60% water, it absorbs signals in the 2.4 GHz band. If the received signal strength indication (RSSI) dips below a certain threshold, the system suggests that a care receiver is near the devices.