In a paranoid state, a man with amphetamine use disorder accused a teenager of hacking into his phone, before tying him up and assaulting him.

The 14-year-old boy, who was high on drugs at that time, complied with Muhamad Zaidi Saleh's instructions to follow him home as he thought Zaidi was a policeman.

Zaidi, 42, was jailed for 15 months yesterday.

He pleaded guilty to assaulting the boy when he tried to obtain a confession from him. Another count of wrongfully confining him in Zaidi's Tampines flat for almost two hours was considered in sentencing.

The court heard that Zaidi had tested "presumptively positive" for amphetamine. But court documents did not state if he had consumed drugs shortly before committing the crimes.

On Nov 18 last year, Zaidi was trying to unlock his Google account outside his flat when paranoia set in, leading him to assume that somebody had hacked into it. His phone received five messages while he was fiddling with it.

He heard a message notification tone coming from a nearby staircase and saw the boy at the void deck. Suspecting him to be the hacker, Zaidi confronted him downstairs at around 12.15am.

Deputy Public Prosecutor Joshua Rene Jeyaraj said the boy was high on methamphetamine, or "Ice", at that time. Zaidi, who did not identify himself, asked the boy to hand over his mobile phone and the boy did as he was told.

"The victim, shocked that the accused had somehow guessed that he had consumed drugs, and worried that the accused might be a police officer, obliged," said the DPP.

Once inside the flat, Zaidi interrogated the boy, who denied hacking into the man's phone. At around 1.40am, Zaidi got some rope and tied the boy's wrists behind his back while the youngster sat in a chair. Zaidi also secured the teenager's legs to the legs of the chair and continued interrogating his victim, who did not resist.

Unsatisfied with the boy's answers, he slapped and punched the teen multiple times. The commotion woke Zaidi's family members from their sleep, and one of them called the police at about 2.10am.

Zaidi freed the boy and allowed him to leave. Policemen arrived shortly after and arrested Zaidi.

Court documents did not state if the authorities have dealt with the boy for drug abuse.

Zaidi is out on bail of $15,000. He will begin his sentence on Sept 22.

He could have been jailed for up to seven years, and fined or caned.