The Pulse resembled a glowing red-and-black meteor or "radioactive conch shell" in its dormant state. It was in the collection of alien collector Henry Parker.
Parker named it and believed it to be a healing device and the only thing that kept him alive despite his ill health. It was not a healing device. Owen Harper later learnt it was actually a reply sent by a race. They had received one of Earth's transmissions meant to discover proof of extra-terrestrial life, made in the 1970s. The Pulse contained a message that was "displayed" in a brilliant light show when it reached full power.
The Pulse leaked dangerous radiation on its first activation in Parker's home. Torchwood stepped in, infiltrated his house and neutralised the device.
Parker died of a heart-attack moments after his conversation about the Pulse with Owen Harper. Owen could not revive him because he no longer breathed and could not perform CPR. Despite this, Owen's mood was improved by looking at the Pulse as it displayed its message. He later shared it with Maggie Hopley — a woman contemplating suicide after the death of her husband. He said if the world could contain something as beautiful as the Pulse, life could still be worth living. (TV: A Day in the Death)