Technologies are generally described for methods and systems effective to broadcast a message. In some examples, the methods may include receiving the message at a modulator. The modulator may receive a power signal configured to provide power to a closed conductive loop. The modulator may modulate the power signal using the message to generate a modulated power signal. The modulator may broadcast the message by sending the modulated power signal through the closed conductive loop. The modulated power signal, when passing through the closed conductive loop, may produce a modulated magnetic wave that includes an indication of the message. A receiver may be configured to detect the modulated magnetic wave from the closed conductive loop. The receiver may be configured to convert the modulated magnetic wave into the modulated power signal. The receiver may be configured to demodulate the modulated power signal to reproduce the message.