Always a great place to go for scientific accuracy… James Bond movies!
Start of Live and Let Die…a British diplomat at the UN is listening to remarks via an earpiece translator. The baddies come into the translation booth and send a pulse and a high-pitched noise through the line that causes instant death in the diplomat.
I suppose they could have just sent a strong electrical current through the line and that might have done it. However, if (as the seen may hint) they used only sound… could you kill someone instantly using sound traveling across a wire? Could a soundwave through an earphone be strong enough to… what, cause a vibration that leads to instant brain hemmoraghing?