Pretending to be interested in a membership, an alleged thief instead cleaned out seven lockers at a gym in Merchant Road on Thursday afternoon, making off with cash, credit cards and mobile devices.
But he was soon tracked down by the trainers and their clients from the Energia Fitness Club in just three hours and arrested by the police.
An iPad, stolen from trainer Gaston Ng, 32, had a location tracking function, which gave away the suspect's whereabouts.
Using an iPhone he still had with him - which had an app that could monitor the iPad's location via a map - Mr Ng found the man.
"I didn't believe the app worked, but we saw him walking up and down Perak Road in Little India," Mr Ng said.
Recounting the incident yesterday with Mr Ng, 40-year-old gym owner Mohamed Fazlon said that after the man left, clients came to him to complain about stolen valuables. Money was also fraudulently withdrawn using one of the stolen ATM cards.
The former bouncer said he remembered a suspicious-looking Caucasian man - who was not a regular - walking in around lunchtime. "He spent 10 minutes in the locker room; I thought he was using the toilet."
He later got an image of the man through CCTV footage. While a police report was lodged, Mr Fazlon decided to track down the suspect.
With Mr Ng, another trainer and two clients, they drove down to Little India. It was along the way that the signal from Mr Ng's iPad disappeared. "It was like a movie. Suddenly, there was no more signal. He may have switched it off," Mr Fazlon said.
But the group persisted, splitting up to scout at mobile-device shops and a nearby hotel. A man matching the CCTV image was found at a shop, trying to sell a laptop.
The police arrived about eight minutes later, Mr Fazlon said, and when the suspect tried to brush off the officer, he decided to step in.
"I appeared in front of him and said: 'Don't you remember me? You went "shopping" in my gym.' I could see his face change then," said Mr Fazlon.
Police searched the suspect's bag and, besides finding various gadgets, also discovered various tools like a crowbar and cutters, Mr Fazlon added.
The police told The Sunday Times that a 59-year-old man has been arrested and investigations are ongoing.