San Diego — In the hot frequencies, the 800 megahertz band, one can hear all kinds of terrible things. Good people and bad people alike victimized by neighbors, lovers, drunk drivers, dogs, drugs, alcohol. On a Monday night in mid-December, I listened to a range of misfortune -- from inconvenience to tragedy.

I heard a road worker complain to his dispatcher about a flat tire on his truck. "Where in the hell," he wondered, "am I going to find a 130 psi tire at night?"

I heard a policeman and dispatcher argue over what word best described a piece of evidence. "So it's a little plastic bag?" the dispatcher asked.

"No," the policeman said angrily. "It's a Baggie. I said Baggie."

I heard a dispatcher hail her officers, calling them to a "critical" situation. A young man, who had been mixing narcotics, had a hammer in hand and was mad. An officer and the dispatcher worried that his dog -- make that K-9 -- had been sent back to the trainer that morning. Should he wait for backup?

I heard an EMT describing an overdose victim as suffering from palpitations and pale, dry skin that was "cool to the touch."

I heard an EMT explain to a dispatcher that a woman had collapsed after a two-day alcohol binge. Her family was at the scene and was despondent because she had just been released from a treatment program. She was lethargic and also "cool to the touch."

I heard about the length and depth of the facial lacerations suffered by a man in a domestic dispute.

By mistake, I swear, I heard cell-phone conversations.

I heard Dennis Miller say something stupid about the football game. That was weird because it was playing on my TV, on mute.

Several weeks before, a well-intentioned friend sent me a police scanner. It came in a box that had Kaczynski written all over it. A mysterious return address. Square and heavy. I opened it outside. It was a Uniden Bearcat BC3000XLT, twin-turbo, 400-channel, 20-bank scanning radio.

Little did I know what a Pandora's box that package was. Over the next several weeks that Bearcat taught me a lot about what I don't know.

I read the operating guide a dozen times. I read the Police Call Frequency Guide two dozen times. I immersed myself in the guide's arcane passages on radio technology. I learned about cycles, frequencies, and wavelengths. I learned about Heinrich Hertz, a 19th-century physicist and pioneer in the study of radio waves, which travel at the speed of light. They radiate out from a transmitting antenna at 186,000 miles per second. I learned that the radio spectrum is divided into many small bands -- entertainment broadcasting, television, ships-at-sea, short-wave broadcast, amateur, aircraft, CB, and so forth. The AM and FM bands are just two small parts of the radio spectrum, which stretches from about .050MHz to 20,000MHz. In its patient introduction to radio for beginners, Police Call explains that a dial for tuning the entire spectrum "would be miles long." I read about simplex, semi-duplex, and full-duplex systems; frequency mixing; decibels; and wick, discone, and beam antennae. I studied the section on "strange sounds": intermodulation, harmonics, spurious signals, false signals, and white noise.

I fancied myself a learned, expert amateur -- a "ham." I went straight to the "800s," where most public-safety agencies broadcast. I picked something up right away: some gang members were loitering around a liquor store. The owner had called the cops. Just when they arrived at the scene and were about to confront the alleged thugs, I lost the signal. My scanner went flying. A new voice came up. It was an EMT. He told his dispatcher the ambulance would get the old man who just suffered a heart attack to the hospital in five -- then I heard Spanish.

Any real ham already knows that I skipped the Police Call section on trunking and that my BC3000XLT is an old, worthless scanner. It's not a so-called trunk-tracker; all I'll ever pick up with it are teasers -- snippets of action. Frustrated, I made some phone calls. The consensus was clear: I was an idiot and knew nothing about police scanning. I needed to go to school.

So I arranged a meeting on December 19 with Roger Williams, proprietor of the Mud Shack, a scanner retail store just east of San Diego State University. Williams has another Mud Shack in Las Vegas, where he lives, but he visits San Diego occasionally to spend time in the local store.

The Mud Shack is located in a small, humdrum mall on El Cajon Boulevard. It's cluttered with scanners -- the latest trunk-trackers and dinosaurs from the early days of scanning -- and all kinds of radio equipment. Antennae, microphones, and wires hang from hooks in the walls and lie loose in boxes. The store has been open for "about 25 years," Williams said, and is a police hangout. A coffeemaker sits on a picnic table at the front of the store, and periodically people come in off the street to grab a cup. Williams drinks coffee constantly.

"Mud," he explained, "is Navy coffee."

Williams is sort of a human scanner, a curious, garrulous man willing to share what he knows, which is quite a bit. He jumps from subject to subject, revealing in about an hour his knowledge of radio, his passion for figure skating, his fondness for Michelle Kwan, and that he is a family man, a straight shooter, and an amateur art collector. The old ham culture, he reassures me, is out there. It's just a game of cat-and-mouse.

Even if a little exasperated with my ignorance, he's a good teacher. He explained to me that almost all public-safety radio systems in the country made the switch to trunking several years ago. (The San Diego Police Department made the change in 1993.) Before trunking, simple crystal radios could tune in to the limited number of frequencies available for public-service radio transmission. As the number of frequencies multiplied, manufacturers developed the scanner, which allowed users to zero in on police- and fire-department dialogue. In the mid-'90s, scanner enthusiasts found that public-safety communications were disappearing from the airwaves. In 1998, Williams explained the effect of trunking in an article he wrote for the Digital Journalist (www.digitaljournalist.org).

"We now listen to a sentence of police talk, rapidly replaced by the dog catcher, then the fire guys come on, only to be replaced by the water department."

Trunking permits a large number of users to share a small number of frequencies. In a trunked system, a single conversation jumps automatically from frequency to frequency -- like a dozen airplanes circling and sharing three runways, Williams said. Trunking was a problem for scanner listeners until the arrival of the trunk-tracker, which, to put it simply, automatically moves the user along to the new talk frequency.

"Mud Shack does not have the capability of releasing all the San Diego police codes to the general public," Williams said. "Media access, of course, is necessary."

While Williams and I were talking, a woman entered the store. She was about 60 and said she lived in Coronado. She needed a new battery for her trunk-tracker. For my benefit, Williams asked her why she listened to a scanner.

"The radio at night is so terrible," she said. "I listen to classical music during the day, but I hate the talk shows at night. I would rather listen to a scanner at night than stare at the ceiling. Sometimes I wake up in the middle of the night and turn it on. It's fun, but you don't get the whole story," she added. "You hear a domestic-abuse case, but nothing about what happens after the arrest."

"It's odd," she said, "but I can't hear anything in Coronado even though I live there. I only hear stuff happening across the bay, safely away from me."

Today, in yet another move to stay ahead of the hobbyists and criminals who use scanners, some police departments are switching to digital communication systems, which are even harder to monitor. The San Diego County Sheriff's Department and the Coronado Police Department implemented digital systems last year. That's why the woman can't monitor the Coronado frequencies.

Considering current anxiety about racial profiling and law-enforcement corruption, some media organizations are concerned that police departments will use digital systems to hide from public scrutiny. An editorial that appeared in the November 27 issue of Editor & Publisher magazine warned, "Even citizens who have no interest in sitting by a scanner listening for the 10-18 'urgent' signal realize society's critical interest in ensuring that news organizations have the tools to monitor how police and public-safety forces are doing their jobs. In emergencies, it falls on the media more than any other institution to get vital information to the public. And, for more than 200 years, Americans have refused to subject themselves to the dangers of secret and unaccountable law enforcement. No mere technology switch justifies trading away liberty."

Pat Drummy, communications manager for the San Diego police, told me on December 20 that the department has no intention of hiding communications from the public -- "quite the opposite," he says -- and isn't planning on upgrading to digital.

"When the digital systems become reliable and stable, we'll change to one," he says. "But we're not comfortable with what's out there, and we would want to be because it would cost between $6 [million] and $8 million to convert. Those who have the new systems do a lot of tinkering, so we'll stick with our archaic system until we find something else."

My investigation into the scanning subculture turned up some odd, paranoid individuals, but no one who seems too worried about losing access to police chatter. One man I spoke to about scanning demanded that I identify him only as a "Washington communications expert with close ties to the current and incoming administrations." He wants to remain anonymous because "the climate in Washington is so weird." He told me I was lucky to be speaking with him at all, as he was about to leave for Hanoi. This raised my hopes that he was about to confess some vast radio conspiracy to me.

"The police are always trying to find ways to hide information from the public," he said. "But the media has adequate access to the San Diego analog system at this time...and the civilian sector does not need to know everything that's going on. Civilians don't need to hear a bank robbery in progress and get any ideas about how to rob a bank. People don't like to be left out, but I believe we have an obligation to protect the public from themselves sometimes."