Abstract: A wireless alert device is paired with a communication device and a connection between the wireless alert device and the communication device is established. The wireless alert device continuously emits a first wireless signal, and the communication device continuously emits a second wireless signal. The wireless alert device receives the second wireless signal, calculates a first received signal strength indication (RSSI) value of the second wireless signal, and sends out an alarm when the first RSSI value is less than a preset value. The communication device receives the first wireless signal, calculates a second RSSI value of the first wireless signal, and outputs an alert when the second RSSI value is less than the preset value.