CAIRO — It is rare that the most important piece of equipment in your bag is the bag itself, even more rare for that bag to be a black plastic trash sack slung over your shoulder as you walk past pro-government thugs on a bridge over the River Nile. The trash bag’s purpose, of course, is to conceal your large nylon camera bag, which is likely to get you grabbed off the street by the aforementioned thugs.

Sometimes the hardest part of a story is getting there. Sometimes it is getting around. Sometimes it is obstructive intelligence agencies and soldiers. Sometimes it is lawlessness, sometimes overattentive law enforcement. Sometimes it is lack of transport, poor communications, power blackouts, accreditation difficulties or a hostile local population.

“At one checkpoint you will encounter a thug with a nail-studded plank; elsewhere, a member of the professional class twirling a golf club, who smiles and remarks, ‘Interesting times, no?'” — Stephen Farrell

Though my colleagues and I have worked in far more dangerous places and under far more primitive conditions, I don’t think I’ve ever before covered a story in which all the above-mentioned obstacles were present and taking turns on a daily — sometimes hourly — basis to become the principal barrier to getting the journalist in and the story out.

No matter how many precautions you take, it is mostly about luck. There doesn’t seem to be a blanket prohibition on journalists. Instead, it is very much a case of one area near Tahrir Square being dangerous and another benign. At one checkpoint you will encounter a thug with a nail-studded plank; elsewhere, a member of the professional class twirling a golf club, who smiles and remarks, “Interesting times, no?”

I was hauled out of one taxi by checkpoint vigilantes and handed over to the police. For some of my colleagues, that has been the first step to a beating, or hours in detention. In my case, however, the policeman spent two minutes looking at the passport and press credentials, and waved me on.

Getting hassled or attacked seems to be a case of being the wrong person in the wrong place at the wrong time. And the closer you get to Tahrir Square, the more likely it is to be all three.

Once inside the square — Liberation Square — you can use whatever equipment you like. Getting it there without being caught is the problem.

So, back to that plastic bag, which, until a few moments ago, was hanging from a railing in the square, dripping something unpleasant.

After the first few days of protests, it was clear that it was risky to be instantly identifiable as a journalist anywhere in Cairo. The state media has been pumping out xenophobic stories about foreign journalists causing all the problems and damaging Egypt’s image. (This in itself will be an interesting dynamic once it becomes clear which has triumphed: the nimble new-media denizens of Tahrir Square or a regime in full control of the official newspapers and television channels, harnessing its power to divide and rule.)

Facing hostile intelligence forces and potentially hostile citizens, I had to lower my profile. Absent a cloak of invisibility, the plastic bag was a decent emergency measure, though hardly practical for long-term use. So I started breaking down my equipment into smaller pieces, to fit into smaller bags that could pass as tourist bags.

Since I started shooting video for The Times in 2007, I have used two cameras: a Sanyo Xacti, when things were really bad in Iraq and it was truly dangerous to be seen out on the streets, and a larger JVC GY-HM100U. I took a JVC to Egypt, with a point-and-shoot Panasonic Lumix DMC-LX3 in my pocket as an emergency backup.

“I broke down everything in my hotel room and replaced it with something that didn’t do the job as well, but did it much less conspicuously.” — Stephen Farrell

The JVC is smaller than the big cameras carried by those who know far more about video journalism than I ever will. But The Times’s video experts have identified it as a useful tool because it has an easy workflow, using SD cards and .mov files that can be dragged straight from the card to your hard disk and into Final Cut Pro for instant editing, and you can strip it down to its barrel in seconds. Once the lens hood, shotgun mike and handle are off and stowed away in pockets or small bags, it looks more like a tourist’s camera than a journalist’s.

So it came to pass, just as Q Division said it would. I broke down everything in my hotel room and replaced it with something that didn’t do the job as well, but did it much less conspicuously.

My Times colleague, Rob Harris, put it well. “It is precisely because you have good equipment that you can operate in loud, crowded situations such as Tahrir Square,” he said. “But they are exactly the sort of things that we can’t be seen carrying now.”

Out went the shoe-mounted camera light for nighttime and indoor interviews, and into the bag went small Petzl headlamps with a bit of orange gel stuck onto the lamp to warm up the light. Not great, but it might make the difference between interviewing a person and interviewing a shadow. And tourists carry them.

Out went the shotgun and lavalier microphones, with their ability to isolate a voice in a crowd and get decent audio. It’s often not wise to waste time on the street trying to clip microphones to people’s clothes or having one more battery-powered device that can fail at the most inconvenient time. (On Saturday, I was atop a high building overlooking Tahrir Square when a general on the ground addressed the crowd through a megaphone. With a shotgun mike, I could have picked out every word. With the nondirectional, built-in mike, however, I could barely hear him.)

Out went proper headphones. They’re far too visible. Earbuds are a decent workaround to isolate what the mike is picking up from ambient sound, especially the very, very loud ambient sound of Tahrir Square.

Out went the tripod. It’s an instant giveaway. I was surprised mine even made it through the airport. My workaround is an Octopod. It can be used to fix the JVC to railings, barricades or anything stable to get a decent, steady, long-range shot; to hold the camera more steadily in a crowd, its legs balanced against my legs or chest; and to raise the camera above onlookers’ head levels, following in the formula (O + OAAH + i) x 10,000. [O = onlooker. OAAH = length of outstretched arm above head. i = iPhone.]

Here’s what cannot be shed.

“When cellphone service and the Internet are switched off, the ‘new media’ revolution in Egypt instantly becomes accessible only to the big, old media.” — Stephen Farrell

Data storage devices like thumb drives, hard disks and SD cards. I try to back up all data immediately and delete it from the cards I carry around with me. Multiple backups can then be kept in different places in case of raids on bureaus, hotels or homes. This is time-consuming and confusing, but gives me more peace of mind.

Three or four phones are still a necessity, in case one gets stolen. Which, of course, happened. Someone liberated my BlackBerry in Liberation Square.

Two satellite phones are in the kit: a handheld Thuraya and a BGAN about the size of a small laptop. In a few minutes, these can go from utterly useless to utterly irreplaceable. (Video files are so large that sending them on a BGAN is like draining Loch Ness through a toothpaste tube, and hugely expensive.)

When the Internet is working in Egypt, the bandwidth is fine and everyone can use Twitter, Facebook and so on to their heart’s content during riots. Indeed, I confidently predict injuries among excitable Twitter users who are so intent on getting the latest development out first that their eyes are cast down to their screens — even as rocks are flying toward their heads.

But when cellphone service and the Internet are switched off, the “new media” revolution in Egypt instantly becomes accessible only to the big, old media who carry satellites with them.

Satellite phones have been an indispensable communication lifeline in a major Middle East capital that deliberately plunged itself back into the pre-digital era to stop the flow of information. Land telephone lines were still up, although unreliable. Without the Internet and digital networks, the flow of data was vastly reduced — which was, of course, the point.

For the moment, governments can still impose such restrictions, although they also hinder businesses, emergency services and people going about their daily, nonprotesting business. Such levels of control will become much less possible for dictators and authoritarian regimes when cellphones or Internet networks have the Thuraya’s capacity to switch from terrestrial communication to satellites, largely bypassing government interference.

Not that governments won’t keep trying to hinder us.

We’re now hearing about a crackdown on the accreditation of journalists trying to get into Tahrir Square. That’s a new one. And so comes another round of this ever-evolving story, as tactics are devised and counter-tactics imposed. This is not over yet.

Stephen Farrell is a foreign correspondent for The Times. He joined the Baghdad bureau in 2007, the same year he began shooting video, and has worked in Iraq, Jordan, Egypt, Afghanistan and Pakistan. He runs The Times’s At War blog from the field, and his latest report from Cairo is “A Night in Tahrir Square.”