"After 2009, most members of Congress stopped making themselves so available," Ruben said.

Rep. Raul Grijalva (D-Ariz.) has come to believe that town hall meetings can be "counterproductive," said spokesman Adam Sarvana, adding that the liberal firebrand sees no need for "the Republicans to show up here to yell at him." Instead, Grijalva has opted for themed meetings, small venues and press conferences.

Rep. Tim Griffin (R-Ark.) has held a marathon of 13 town halls in his reliably Republican district this recess. But the threat of yelling activists was on his mind: He began several recent forums by mentioning a MoveOn.org primer on disrupting events.

"I referenced to it and said, this is what some people are trying to do," Griffin said. "I just want everybody to be heard, to be civil and respectful."

Being mobbed by protesters in 2009 hasn't stopped Rep. Tim Bishop (D-N.Y.) from holding traditional town halls, said spokesman Jon Schneider. But Bishop has spent most of his time meeting with constituents one on one and making casual appearances this recess.

FreedomWorks has developed an online networking tool, called Freedom Connector, that helps users find nearby conservative activists, groups, and events. Liberal blog the Daily Kos has linked to Freedom Connector as a source of information on when and where to find elected officials.

The situation doesn't mean lawmakers aren't meeting with constituents--they are. But scheduling quirks like charging for events, timing events inconveniently, and hosting events for specific interest groups have helped lawmakers limit their exposure to confrontational constituents.

Congressional aides insisted that their events are well publicized through e-mail, website announcements, or alerts in local newspapers. They cited scheduling issues as the top reason for announcing an event on short notice.

But not all members make their schedules public. The office of Rep. Dave Reichert, (R-Wash.) declined to release his schedule of events.

"Aside from various other tours and visits in the community, we are currently planning his tele-town hall schedule," spokesman Charles McCray wrote in an e-mail. More than 200 protesters gathered outside Reichert's office on Thursday, the third such incident this month.

Some legislators are, and always have been, bigger fans of the town hall format than others. Politicians who were narrowly elected in 2010, or faced contentious battles in swing districts, perhaps have the biggest incentive to avoid bad publicity. But now that "town hall meeting" has become a synonym for "angry shouting match," politicians of all stripes are approaching the venue with caution.

High-tech alternatives, like "tele-town halls," have emerged as something of a double-edged sword for elected officials. The mass conference calls are an easy, low-cost way to reach hundreds of constituents, but they've been criticized for being "a little bit more easily manipulated," said Norman Ornstein, an expert on Congress at the American Enterprise Institute.