Police detectives working under cover arrested a 26-year-old woman in the Clarendon Hill Towers apartments, charing her with sexual conduct for a fee.

Police made the arrest Aug. 19 at about 7 p.m. as part of an ongoing effort to curb the illegal sex trade in Somerville, according to a police report.

The report says detectives responded to an online advertisement offering "services for a fee."

One detective posed as a potential client, and after numerous phone conversations with a woman, he was instructed to knock on the door of an apartment in the Essex Building in the apartment complex, according to the police report.

Once in the apartment, the woman questioned the undercover detective about his employment status, according to the police report, which says this is a tactic commonly used "by individuals involved in this type of activity to root our unwanted police intervention."

When the woman was convinced the undercover detective wasn't a cop, she accepted $160, said she would make it worth the detective's while, and handed him a LifeStyles Ultra Sensitive condom before removing all her clothes, according to the police report.

The undercover detective then gave a predetermined signal and the surveillance unit, which was waiting in the hallway, arrested the women, according to the report.