Whenever she was at home, she would notice men entering the next-door flat at hourly intervals.
The 58-year-old teacher said that though her two neighbours had been living in the four-room HDB flat since January, she hardly saw them. Once, when she saw one of them and tried to talk to her, the woman scurried away without saying anything.
On Tuesday, police arrested the two women from China, aged 28 and 44 years, for alleged involvement in vice-related activities at their flat in Woodlands Drive 14.
The arrests were part of a 22-day anti-vice operation, which ended on Tuesday.
Officers from the Criminal Investigation Department and the six Police Land Divisions took part in the raids at multiple locations, including residential units and condominium developments. The areas included Clementi, Jurong West, Sembawang and Yishun.
A total of 134 men and two women aged between 23 and 50 years old were arrested.
Flat owners are encouraged to check on their tenants regularly to ensure that vice-related activities do not proliferate in residential estates, said the authorities. Tenants caught misusing their flats will not be allowed to rent an HDB unit for five years.