Dr. Conrad Murray used a cheaper model of a pulse-and-blood-oxygen monitor when another model, available for $40 a month, would have alerted him that something was wrong with Michael Jackson, a representative of the equipment manufacturer testified on September 30, 2011.

Robert William Johnson, who works for the medical equipment company, Nonin Medical, said the $275 model used by Murray was "not labeled for constant monitoring" of a patient and should have only been used for spot checks.

The other model, a device that cost $750 and could have been leased at $40 a month, had a "loud and annoying" alarm that could have been heard outside the room, Johnson said.

In cross-examination, Murray's attorney, Michael Flanagan, asked if the "the only difference" between the models would be that the cheaper device would need to be continuously watched by the physician. Williams said yes.

Prosecutor David Walgren countered by asking: "That's a big difference, right? ... Between life and death potentially?"

"Yes," Johnson responded.

Johnson was the first witness to testify Friday in the trial of Murray, Jackson's personal physician who faces an involuntary-manslaughter charge. Murray is accused of administering a lethal dose of the surgical anesthetic propofol that led to Jackson's death.

Other witnesses expected to testify Friday include a patient of Murray's, and paramedics who testified at an earlier hearing that they arrived at the singer's Holmby Hills mansion to find Jackson lifeless and his doctor evasive.