Generally, when a vampire brings a human across death’s door into the dark bloody shadows they relay the history of their sire line. Even if this history wasn’t shared vampires can go into a deep meditative psychic state and discover the vampire family they came from. This even includes the demon patriarch who started everything by deeply possessing a human and mating with another to create a first generation vampire. They, in turn, can transform vampires the old-fashioned way. It’s the demonic energy that bonds all successive generations of vampires thereby giving them a psychic connection. These supernatural connections are used to telepathically communicate with their vampire relatives around the world. Most often occurring as they sleep.
If a related vampire is dead then they can communicate with them if they became a demon in Hell. However, if they embraced their humanity and went to Heaven then the bond is lost. If their dark soul ended up in purgatory or somewhere else they would also lose the demonic bond. These psychic bonds were especially important before global communications. Since Immortals vampires would globe trot around the world it would be easy to lose track of vampire family and friends through the centuries. Without telepathic communication trying to find them would be like looking for a needle in a haystack!