IT designer Charl Johnson feels his privacy was compromised after his cellphone number was read out in the High Court in Pretoria during the murder trial of Oscar Pistorius.

"It keeps on ringing so I keep it off... I feel my privacy has been compromised severely," he told the court on Wednesday.

Johnson's cellphone number was read out in court on Tuesday.

He said a number of voice mail messages were left on his phone after it was read out, including a message asking him why he was lying about what happened on the night that Pistorius killed his girlfriend, Reeva Steenkamp.

The third day of the trial got underway around 9.30am.

Judge Thokozile Masipa asked Johnson to speak a bit louder after he took the stand.

On day two of the trial, Johnson testified that he and his wife Michelle Burger were woken up by piercing cries, followed by gunshots in the early hours of Valentine's Day last year.

Johnson's testimony corroborated in detail what Burger had told the court on Monday.

Pistorius, wearing a black suit and carrying a laptop bag, arrived at the court around 9.10am on Wednesday surrounded by police and security. His family entered a short while later.

Pistorius, 27, is accused of murdering Steenkamp on February 14 last year.

He has pleaded not guilty to the charge of murder, and to contraventions under the Firearms Control Act.