Patong police said that Rangsit Jannon, 19, went to the Thongsakuna gold shop in the Nanai area of Patong about 7pm and asked to look at necklaces.
He was shown one, worth about 26,0000 baht. He took the necklace, ran to his motorcycle parked outside, and rode off.
About 11pm, officers arrested him at his apartment not far away.
Police claim the number of crimes in Patong, on Phuket's west coast, have fallen by about 30 percent since the Safe Patong campaign divided the city into six zones and activated community groups who stay alert for unusual events.