“That is sort of an antiquated way to look for a device,” Mr. Zabel said.

Federal prosecutors have charged Mr. Tabone, vice chairman of the Queens Republican Party, with bribery and wire fraud for allegedly taking cash in exchange for using his influence to secure a ballot spot for State Senator Malcolm A. Smith, a Democrat, in the Republican primary for mayor. Mr. Smith, along with a Republican city councilman, Daniel J. Halloran III, and a Republican Party leader from the Bronx, Joseph J. Savino, were also charged. The criminal case was built, in large part, on secret recordings.

It was the first of two instances last week where federal prosecutors unsealed a criminal complaint against New York political leaders, using their own words against them.

On Thursday, two days after the corruption case centered on Mr. Smith’s mayoral aspirations became public, the United States attorney in Manhattan, Preet Bharara, announced new charges in an unrelated bribery case. In that case, cooperating witnesses, including Assemblyman Nelson L. Castro, who has since resigned, wore devices to record conversations that led to the arrest of Eric A. Stevenson, a Democratic state assemblyman who was accused of accepting more than $22,000 in bribes to help developers open adult day care centers in his district in the South Bronx.

In one recording, officials said, Mr. Stevenson invokes previous scandals in Albany and openly worries about being taped. “Be careful of those things, man, the recorders and all those things,” Mr. Stevenson says to a cooperating witness, according to the criminal complaint.

Mr. Zabel and other federal officials declined to reveal exactly how the recordings in the two recent cases were made. “We don’t want people to know what we can do, but we don’t mind people thinking that we can do all kinds of things,” an F.B.I. spokesman, James Margolin, said last week.

As for the recordings of Mr. Tabone and other suspects in the two cases, Mr. Margolin said, “I presume that it wasn’t the kind of devices that we used in the 1980s,” similar to the one depicted in movies like “Prince of the City,” the 1981 film starring Jerry Orbach and Treat Williams, who plays a New York City narcotics detective who wears a wire to expose police corruption.