Contra Costa- Early in his career, sheriff’s vice Detective Andy Van Zelf figured out how to infiltrate massage parlors that were providing a bit more than a back rub.

For years, Van Zelf and other undercover Contra Costa sheriff’s detectives have slipped into those businesses, often located in strip malls, and asked for a massage. If the masseuse agrees at any point to manipulate below the belt, the cops utter a code word into a wire and are rescued by their uniformed colleagues.

Van Zelf said the women have altered their techniques over the years — techniques in avoiding law enforcement, that is. They whisper so the wire won’t pick up their voices, they keep the wads of cash they’ve collected off-site, and they keep staff to a minimum. The pimps don’t come around much anymore, Van Zelf said.

But after years of getting busted for prostitution, the illicit operators have hatched a new way to hide from the law in the suburbs: attracting customers to apartment massage parlors via the Internet.

“Like anything else, they’re evolving,” said Van Zelf, who first noticed the apartment-based operations about a year ago. “As the criminals get better, so do we.”

San Ramon police recently made their first bust of an apartment-based illegal parlor. After a monthlong investigation, they raided an attractive ground-floor unit in the expansive Promontory View Apartments off Deerwood Place. They arrested on suspicion of prostitution a Korean national with no local address who called herself Gigi.

The woman was booked into County Jail and released when no charges were filed, although police say the charges are pending.

The apartment was being used as an “apartment massage parlor,” a type of business that is widely advertised on Bay Area Web sites and provides anything from sensual massage to sexual intercourse.

“It’s just really an apartment that consists of mattresses on the floor,” said Detective Rachelle Davies, one of the San Ramon officers investigating prostitution in town.

Late last year, Davies and Sgt. Joe Gorton were on the trail of an apartment parlor operated by a group that calls itself Korean Pleasures. One day, the operation was gone, Gorton said.

When it resurfaced in Dublin, police there shut it down, but “within two months, that same group moved back to another apartment in San Ramon,” Gorton said.

That was the Promontory apartment. Police, watching for their return, set up the sting.

Using a stand-alone computer at the investigations bureau to get around department Internet filters, Davies and Gorton browsed the Web looking for explicit massage parlor ads.

“I know that if you have a scantily clad woman showing other stuff, you’re not necessarily going to go there to just get your back rubbed,” Gorton said, clicking through some of Davies’ bookmarks.

They started at well-known sites offering classifieds that include massage parlors. Their surfing led the officers to the San Ramon location of Korean Pleasures. The business also has locations in Richmond, Mountain View and other Bay Area cities.

“We monitor it on a regular basis because we don’t want a problem,” Gorton said.

After sheriff’s deputies busted storefront massage parlors in Danville and Lafayette in March, several new illegal operations opened in apartments, Van Zelf and Gorton believe.

Contra Costa District Attorney Bob Kochly said he has filed charges on more street prostitution cases than Internet cases.

“My experience in our county is we’re talking about drug addicts who are trying to make money to support their drug habits,” Kochly said of prostitutes.

The massage parlor operations are not as pressing an issue for law enforcement agencies, Kochly said, because they are not out in the open.

But he said any type of prostitution raises quality-of-life issues for area residents. Gorton echoed that concern.

“They really have more of a detrimental effect as far as the quality of life,” Gorton said.

Although apartment-based prostitution is more discreet than street prostitution, it is more visible to families and children living nearby, Gorton said.

Since women are not standing on the corner soliciting in places such as San Ramon, the solicitation occurs online and by cell phone.

Gorton said clients call the number on the Web site and get an approximate location for the apartment. When they get there, they have to call a second time to get the exact address.

“There’s a community out there, for lack of a better term, it’s a hobby for them,” Gorton said.

This “community” has kept in touch via the Web since 1997, trading tips on what certain “girls” will do, rating the women they see, philosophizing on the merits of prostitution and trying to avoid the scrutiny of police, wives and girlfriends.

“I am one of the (clients) that had visited KP (Korean Pleasures) over 50 times all the way back to the old Emeryville location and had also been to KPSR (San Ramon) a number of times earlier this year,” one active client told the Times by e-mail.

He said there have been apartment parlors in Berkeley and San Francisco for at least two decades but they may be relatively new in Contra Costa.

The patron, who would not identify himself, said he is a 40-year-old East Bay mechanic who owns his own shop and has been paying for sex since he was 16.

He also said he’s married and has a child.

“If I didn’t have the spare coin in my pocket to dabble in something like this, I’d probably curtail it,” the man said in a phone interview, likening the addiction and expense to indulging in cappuccinos at the local cafe.

Men give all kinds of reasons for paying for sex, said Van Zelf, who has run across many “johns,” but the bottom line is it’s illegal.

“I’m not a doctor,” he said, “I’m a cop.”

Davies and Gorton said they are investigating other apartment massage parlors in San Ramon and hinted they may set up their own operation to deter the clientele from visiting their city.

“I don’t think that it’s a very healthy hobby,” Van Zelf said.