“Pulse” is episode six of season one of Threshold.
In Miami, at an underground rave, the music that the DJ is playing turns out to contain the alien signal. The situation rapidly degenerates, and many are rushed to hospital – it seems that mind-altering pharmaceuticals and DNA-altering alien sounds don’t mix that well.
The Threshold team travel to Miami to get control of things, as there’s the potential of hundreds of infected ravers starting to spread the signal, which would rapidly become extremely bad. It turns out that the DJ’s brother was on the freighter which encountered the UFO, and he had rung her up during the event. Which means that she was exposed to the signal, too, and had recorded it on her answering machine.
Even worse, it seems that the signal is self-propagating, spreading itself to other devices, without anyone needing to spread it. Sort of like a computer virus, only far more aggressive and independent. With it being on potentially hundreds of electronic devices in the Miami area, some more extreme measures are called for.