Call it the Butterfly Radio: in Frequency, a guy discovers his old ham radio can talk to his dead father, 30 years ago. And this causes endless time-paradoxes, including a serial killer. Good thing the 1960s dad is Dennis Quaid.
After talking to Quaid earlier today, we couldn't help watching him as the 1960s Queens everyman in Frequency, where his grown-up son starts babbling at him over the radio about baseball scores and who's going to die when. The son (played by Jim "Outlander" Caviezel) manages to save Quaid from dying in a warehouse fire, but through a kind of twisty movie logic, this leads to Quaid's wife being killed by a serial killer the following week. It never fails: You mess with the timelines, you get serial killers. It's all worth it for the above clip, where Caviezel has to explain the situation to Quaid. Who just takes it on board, because he's a mensch.