Systems and methods for controlling power on a communication network bus connecting an auxiliary device and a control device in a pool or spa system. The control device includes a power source for providing voltage to the device and a power detector. The auxiliary device can provide additional voltage to the control device via the communication network bus. The power detector may be capable of detecting voltage received by the control device via the communication network bus. The power detector may also be capable of detecting traffic (e.g., communication) by the control device or the auxiliary device via the bus and/or data collision on the bus. The power detector is configured to enable or disable the power source of the control device based on voltage detected on the communication network bus, traffic detected on the communication network bus, and/or data collision detected on the communication network bus.