Hand signals are passed from the rooftop spotters to the street protesters below: Another group of riot police are moving in their direction.
"Wait," one of the rioters on 443 Lane urges. "Wait. OK, now." The gangs send a barrage of stones toward the police squad's white helmets and then scatter over alleyways and race into homes.
For months, scenes like this have defined Bahrain's Arab Spring unrest: mobs demanding equal rights for Shiites waging hit-and-run battles against security forces defending the Sunni rulers in the tiny Gulf kingdom. In size and fury, the confrontations might seem like little more than a Middle East sideshow in comparison with the far bloodier upheavals in Syria or Yemen.
But in compact Bahrain _ with protest hotbeds and loyalist bastions almost within shouting distance _ everything is amplified. On an island no bigger in area than New York City, majority Shiites and Sunnis backing the ruling dynasty are increasingly unable to find common ground or even agree on a general path toward dialogue.
Protesters are now raising the battle cry of reclaiming Pearl Square, the former hub of the 7-month-old rebellion that's now guarded as tightly as a military base. Security forces, meanwhile, are pushing back harder _ even arresting at least 45 women and girls last week on suspicion of stirring up anti-government dissident in one of Bahrain's main shopping malls.
If Bahrain tumbles toward greater confrontation, places such as 443 Lane will be the training grounds for both sides.
The short street _ jutting off a main road in the mostly Shiite neighborhood of Sanabis _ has been so often caught up in the street skirmishes that used tear gas canisters are collected and stacked in neat rows inside doorways. By late afternoon, the protesters usually begin to gather. Many are well-prepared for the expected tear gas: Wearing swimming goggles and surgical masks. Refrigerators in safe houses hold extra cartons of milk to wash away the burning residue on their faces.
Police appear to have orders to move in at the slightest whiff of a challenge.
And on this night, protesters were particularly anxious for a fight. Voting had just closed in special parliamentary elections Saturday. The voting was called to fill 18 seats _ nearly half the 40-seat chamber _ abandoned by Shiite lawmakers to protest the crackdowns that include deadly clashes and life sentences for some activists.
Shiite groups pressed for a boycott, which they say held turnout to only about 17 percent. Authorities tally it up differently _ portraying the new parliament as representing more than half the country's voters by combining the figures with results from last year's election.
This is part of the separate narratives that make Bahrain volatile and unpredictable.
Shiites claim they are stuck in a permanent underclass although they represent about 70 percent of Bahrain's 525,000 citizens. In their view, all the routes to power, such as high political or military posts, have been blocked by the Sunni leadership. "Welcome to Arab apartheid," read a message spray-painted in red in Sanabis.
Bahrain's Sunni rulers say their country is being pulled apart by rejectionist groups that have chosen violence over dialogue, including offers to allow parliament to vet government appointments such as the premiership. They also view the main Shiite political blocs as deeply conservative _ with ties to Shiite leaders in Iran and Iraq _ and a threat to women's rights and Bahrain's open economy.
The leadership's stance is hardened by the belief that Shiite power Iran is plotting ways to gain influence through the discord in Bahrain _ which could have ended up part of Iran if a U.N.-backed fact-finding mission in 1970 found majority support for annexation.
The fears about Iran also resonate strongly with Bahrain's allies. Neighboring Saudi Arabia led a Gulf military force that came to the rescue of Bahrain's monarchy in March. Washington has stuck by Bahrain's rulers to preserve crucial partnerships, including the base of the U.S. Navy's 5th Fleet. At some police checkpoints, the green Saudi flag flies alongside the red-and-white colors of Bahrain.
On 443 Lane, there are no nuances. The protest gangs see this as their Arab Spring moment that may not come again _ with many too young to remember the last serious street clashes in Bahrain in the 1990s.
But what they want is far less clear. They all denounce the stewardship of Bahrain's king, Hamad bin Isa Al Khalifa, yet have no alternative leader or plan to follow. The driving force of the moment appears to be trying to recapture the mass energy of Pearl Square during the first weeks of the revolt in February.
Authorities know this well. Checkpoints and pincer-style patrols are used to keep protesters mostly contained to their neighborhoods and unable to join forces.
When police moved down 443 Lane, the mobs were ready. First they showered the unit with stones and then took shelter behind metal trash bins overflowing with garbage. Officials have apparently slowed _ or halted _ trash collection in some areas as punishment for the clashes.
Police answered with tear gas.
"Run, run," the protesters yelled. "To the house. The door is open."
About a dozen protesters tumbled through a metal door into the house of a sympathizer. Moments later, the police patrol swept past.
One demonstrator, Ali, poured milk over his face to neutralize the stinging power of the tear gas. He then joined the others on the roof, where they passed signals to other protest sentries tracking the police movements. On cue, some protesters hiding in a pigeon coop rained stones down on the police _ whose ranks include officers from other Arab states and south Asia who are given citizenship under programs to boost Sunni Muslim numbers.
"We know these kinds of fights will not bring down the regime," said Ali, a 27-year-old construction worker who only gave his first name for fear of later reprisals. "But it sends a message that we are here and we will not rest. We feel we are under occupation by a system we no longer respect."
Ali made his way to Sanabis from an area about 10 miles (six kilometers) away, using an underground system of houses that provide shelter and food for protesters. Sanabis is less than a half-mile (one kilometer) from Pearl Square, but they know that it would take a protest army of thousands to break through the cordon of armored vehicles and razor wire.
"Ok, maybe not today. Maybe not next week. Maybe not even next year," he said. "But how long can they protect it? Forever? We will be back in the center of the capital someday."
The storming of Pearl Square by security forces in late February was the first major bloodshed of the unrest. Since then, more than 30 people have been killed.
"All clear," said one of the protesters in the house. "Let's go."
The group slipped out and moved through the darkness of 443 Lane. Someone had just spray-painted a fresh stencil of the tripod-shaped Pearl Square monument, which was razed by authorities after they took back control of the area.
The protesters moved to another building's rooftop to regroup with others before making another run at the police.
They pressed against the walls as a police helicopter passed low overhead. A few blocks away, a store was burning. The smoke was picked up by the wind and carried toward the brightly lit skyscrapers in Bahrain's business district.