Every 95 minutes, the Chinese satellite Zhuhai-1 02 makes a full pass around the planet, its solar-panel arms extending from its boxy body as it observes Earth. Sometimes, its path takes it over Pueblo, Colorado. There, more than 300 miles below, Mike Coletta’s receiving station can pick up Zhuhai’s transmissions. Because as sophisticated as space technology is, the terrestrial tech necessary to make contact with celestial satellites is surprisingly low. Coletta just has four TV antennas—the kind that look like 2-D pine trees—each pointed in a cardinal direction. They’re bolted into place along garage beams, a patio post, and the rooftop of his house.

Inside his home office, on Tuesday, Coletta waits for Zhuhai's signals to appear. He sits in front of a laptop and an iPad, a big shelved monitor hovering above. Coletta has, since 2012, spent his free time eavesdropping on the sky, picking up satellite signals—signals that, for the most part, were never meant for him. He’s listened in with an antenna made of coat-hangers and moulding. He's done it with a rabbit-ear antenna, and with wire taped to yard-sticks. And now, he primarily does it with his quartet of TV antennas—the fanciest setup he's ever had, and still a steal at around $300.

Turning to the iPad, he watches an icon that shows Zhuhai's path across a digital globe. It hops its way in discrete digital steps across a red ellipse that delineates his antenna's field of view. He fiddles with the laptop's settings, adjusting the displayed frequency range and the volume. Soon, a staccato leitmotif comes from the speakers, accompanied by little line segments on the screen—the kinds of data he sonifies, then posts to Twitter and, in earlier days, to his website www.gosatwatch.com, like little space symphonies. This signal looks and sounds like Morse code.

“That’s the beacon,” he explains.

But soon the signal has faded out, as Zhuhai-1 02 passes beyond the domain of Coletta’s detector. He looks over and smiles from inside his beard, then looks back down to see whether another sat might soon pass over.

Coletta is exactly the person you’d expect to build a satellite detector out of Walmart parts. He's worked on space launches and missile warnings, systems that track stuff with big radar systems and radio dishes. He's worked support for Cheyenne Mountain, that impenetrable cave-city for space surveillance. And in his off-hours, he was a HAM radio guy.

While lots of hamateurs are in it for the conversation, Coletta was never so keen on “talking to a bunch of people who talk about their radios all the time.” He mostly wanted to see how far away he could broadcast and receive. So when he discovered he could receive signals from beyond Earth itself, that was the direction he went. Up.

The first hint came from the Space Fence, an Air Force radar system built to detect and track satellites. He first read about it in technical manuals at work around 2012, then started researching online. The fence's transmitters beamed up radio waves that spread into a fan shape, blanketing the continental US in a kind of radio force-field. When an object encountered the radio waves, its body reflected them back to the ground, where six receiving stations picked them up.

Coletta wondered if he could build his own receiving station, and pick up pings himself. After all, a radio antenna is a radio antenna, whether you're getting "How's it going, KM0MMM?" from Michigan or "beeeeeeeep" reflecting off a Lockheed Martin creation. He knew all he needed was wire, cut to the correct lengths—exact fractions of the main radio wavelengths. So he snipped some coat hangers, bent them straight, taped them to a piece of wooden moulding, and mounted the strange spear on a tripod. He added an amplifier and a receiver, which boost and digitize the radio waves, and hooked the antenna into his computer.