After a robbery at a Fairfax County poker game last week, players of the wildly popular Texas Hold 'Em games around the region are watching their backs at the poker table.

On Sunday, a pair of masked men -- one wielding a shotgun and the other, a pistol -- forced their way into a house in the Fair Oaks area where a tournament was being held, police said. Police said they have not had any other reports of Hold 'Em holdups.

Even so, with so many poker tournaments taking place in private residences, with the time and place disseminated through word of mouth or on the Internet, some enthusiasts said they will play their cards a little closer to the vest from now on.

"I know to be careful or be wary when I go to a casino, but at someone's house, you definitely don't expect to have to have your guard up," said Joe Graziani, 33, of Potomac, who plays a game at least once a week with nine people at a friend's house in the District. "If this continues to happen and there's a rash of games getting robbed . . . that would concern me."

The players at the Fair Oaks game were just wrapping up when the armed men burst into the house about 11:20 p.m. and announced a robbery, police said. The two men made off about $5,000 and several cell phones, watches and car keys.

No one has been arrested or identified as a suspect in the home invasion, police said.

At some games in the region, where there are scores of players and the buy-in could be $500 or more, some hosts will hire security guards, said Erik Kroner, 29, an audio equipment businessman who plays a weekly game and recently hosted a 40-person tournament at his Lorton home.

"I know of a couple games that hire security guards. One's at the Watergate. Then there's this one at a residence in the Alexandria area," he said. "The people who play feel more comfortable knowing someone there is acting as security. It's normally for the players' security of mind."

Kroner said he was startled that people would dare to pull off such a heist at someone's house. "It seems to me like an awfully low return for such an incredibly high risk," he said. "If I want to be an armed robber, I am going to go for a bank, not for some poker game that has two or three thousand dollars. For all you know, [the person hosting the game] owns a gun. It seems insane."

Police in numerous jurisdictions in the Washington area, including the District, Montgomery and Prince William counties, said they were not aware of any poker robberies in their areas.

"I can't be sure that it was the first one," said Mary Ann Jennings, a Fairfax police spokeswoman, "but we haven't seen any kind of rash."

The house, in the 3800 block of Alder Woods Court, might have been targeted, or so the host speculated online at the social-planning Web site, which he used to invite more than 280 people to the tournament.

"It is obvious that the men had access to the invitation or were helped by someone on this . . . list," the homeowner wrote, adding that he no longer would host games nor attend games at houses in the area. "It is obvious that these people know about the other games in the area, and who knows when or if they will strike again."

Kelly Young, 38, an office manager at the Washington City Paper who plays in a game once a week, said it can be problematic when people advertise their games through e-mailed invitations, not only because the size and stakes can grow exponentially but also because word of the game can leak to friends of friends of friends and so on.

"People are holding open games that are wide open and not necessarily just for friends," he said. "No one is going to steal $5 bets in the basement, but if I've got 30 to 100 people hanging out with a couple thousand dollars, that's a different story. But then again, if I am going to be doing that card play for serious money, I'll just go to Atlantic City."

Jennings said police continue to investigate the case, including whether any laws were broken during the tournament. It is illegal in Virginia, she said, for the host of any gambling game to take a cut of the winnings. It was not known if that occurred.

On the posting, in which the host announced he would no longer hold tournaments at his house, he wrote that nobody was injured during the robbery.

But "I can truly say the night was a life-changing one," he wrote. "I hope the $5,000 is worth putting seven people through one of the worst nights of their lives and forever ruining what is suppose to be a fun game."

Many poker tournaments take place in private residences, with the time and place disseminated through word of mouth or on the Internet.