Abstract: An indoor unit included in an air conditioner that includes an outdoor unit includes a power receiving circuit (PR2), a low-frequency transmission and reception circuit as a first reception circuit, a high-frequency transmission and reception circuit as a transmission and reception circuit, and an inner-controller. The low-frequency transmission and reception circuit receives a current signal transmitted from an outdoor unit by using a current loop formed by a power line included in power supply wiring. For a first communication state in which physical connection between with the outdoor unit is recognized and a second communication state in which communication for operation of the air conditioner is performed between with the outdoor unit, the inner-controller selects use of the low-frequency transmission and reception circuit and the high-frequency transmission and reception circuit in the first communication state and the second communication state.

Abstract: In a device network system, system recognition processing that identifies a device connected by a wired line is performed using a low-frequency signal of a frequency lower than a first frequency used in communication, and a signal of the first frequency is used to transmit predetermined instruction information. The low-frequency signal includes first information for connection to a network, and identification information of a group to which a device to which the low-frequency signal is transmitted belongs. The predetermined instruction information is transmitted to a device that has received the low-frequency signal, has registered the first information, and has connected to the network, and for which participation in the network has been approved.

Abstract: In a device network system, system recognition processing that identifies a device connected by a wired line is performed using a low-frequency signal of a frequency lower than a first frequency used in communication, and a signal of the first frequency is used to transmit predetermined instruction information. The low-frequency signal includes first information for connection to a network, and identification information of a group to which a device to which the low-frequency signal is transmitted belongs. The predetermined instruction information is transmitted to a device that has received the low-frequency signal, has registered the first information, and has connected to the network, and for which participation in the network has been approved.

Abstract: An air-conditioning apparatus includes a first transmission channel, a plurality of second transmission channels different from the first transmission channel, a controller connected to the first transmission channel and not connected to the second transmission channels, a plurality of air-conditioning indoor units connected to the second transmission channels and not connected to the first transmission channel, and a plurality of air-conditioning outdoor units. The plurality of air-conditioning outdoor units electrically connect the first transmission channel and the second transmission channels, and do not transmit a short-circuit state occurring in one of the first transmission channel and the second transmission channels to a transmission channel other than the one of the first transmission channel and the second transmission channels, thereby enabling communication between devices connected to the transmission channel other than the one.