"People don't wake up from defibrillation and say, 'Thanks, I needed that,' " said Frank J. Poliafico, former director of emergency medical services for New York City.  Such critics are not comforted knowing that at least two over-the-counter competitors to HeartStart Home may reach the market this year.  In response to the critics, Philips says that its product's training material emphasizes the need for calling 911 and using CPR. It also has a recorded voice that prompts users to call 911 and coaches them on CPR - although those commands are not given until after the device has diagnosed whether a shock is needed and, if so, has instructed the user to administer the shock.  Philips says that HeartStart's design reflects its extensive consultation with the Food and Drug Administration.  The company, a unit of Royal Philips Electronics that also makes various professional-grade HeartStart defibrillators selling for as much as $25,000, says it has sold several thousand HeartStart Home units since the F.D.A. approved nonprescription sales last September.  The entertainment world has taken note. The character Leo McGarry, the presidential aide on NBC's "The West Wing," received a HeartStart Home from his staff in an episode broadcast in January.  But Philips cannot cite a real-life example of anyone's being revived with the nonprescription HeartStart Home, or with one of the 5,000 home units sold from 2002 through last fall that required a prescription.  Wendy B. Katzman, business director for HeartStart's home defibrillator business, said that while a life might be saved at any time - a revival at Grand Central Station occurred within days of the introduction of defibrillators there - the company was not counting on instant success stories.  Philips defibrillators were aboard American Airlines planes for more than a year before a life was saved, she said. HeartStart Home is already being offered at a discount - $1,495, for example, on Amazon, which says it has sold more than 1,000.  HeartStart's fans include Douglas R. Bolt, a 49-year-old owner of auto parts and car repair businesses in Orlando, Fla., who bought his unit in February from a local Philips distributor for $1,600. While Mr. Bolt's wife, Terri, calls his HeartMate his "new toy," he praises the product as a potential lifesaver. Mr. Bolt had seen similar devices at the local Y.M.C.A. and already been trained to use them three years ago when he took a Red Cross lifesaving course.  But many are not as enthusiastic. At a dinner party, when he brought out the device in its lunch-box-size case and persuaded a wary guest to conduct a simulated rescue, people saw it mainly as a novelty.  The guest followed the recorded step-by-step spoken instructions, extracting the adhesive shock pads and attaching them to the correct spots on a training mat depicting a man's torso. Then she waited while the device analyzed whether the simulated victim's heart was beating. After it determined that the mat was in cardiac arrest, she executed the device's command to press a flashing orange button with a lightning-bolt symbol. In actual use, an electric shock would have been delivered to the victim's heart.  Once it began reciting the CPR instructions, Mr. Bolt turned off the device, convinced that he had made his point. "I thought they'd ask where they could get one," he said. Instead, the guests were merely amused and, noting that Mr. Bolt was in good health, wondered why he needed a HeartStart Home in the first place.  Some experts deem that a worthy question for any maker of the devices, known as automated electronic defibrillators, or A.E.D.'s.  "We don't know how often cardiac arrest in the home occurs when there is a witness who could use an A.E.D.," said Mary F. Hazinki, a spokeswoman for the American Heart Association's emergency cardiovascular program. "There's insufficient scientific data to recommend for or against A.E.D.'s in the home."  Critics like Dr. Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania, say that marketing such devices preys on the fears of basically healthy people, the vast majority facing little risk of sudden heart stoppage.  The F.D.A. defends its approval of HeartStart Home. "It's been demonstrated to be very user-friendly," said Megan Moynahan, the branch chief overseeing defibrillators and related devices, "and there's no reason to believe it would behave differently in the home than it has in public places, where even untrained people have been able to save lives."  The overall market for external defibrillators has grown 30 percent a year recently and is expected to reach $250 million this year, said Nathan H. Cohen, a market researcher with the consultant Frost & Sullivan.  Philips and other manufacturers assume that the devices could turn into a billion-dollar market if consumers could be persuaded to view them as standard home safety products like fire extinguishers. They know from experience that obtaining F.D.A. approval to sell nonprescription versions was essential to this strategy.  "Seventy percent of people who responded to HeartStart infomercials with a credit card couldn't get a prescription from their doctor," Ms. Katzman of Philips said of the older models.  John J. Kelley, a semiretired owner of an insurance agency in Lorain, Ohio, said he had been reluctant to buy an automated electronic defibrillator as long as he needed a prescription. "I have nothing wrong with me, or my wife, or my family," said Mr. Kelley, who purchased a HeartStart last month on the installment plan through a Philips toll-free phone number. "I didn't want to sound like a hypochondriac."  Competitors are racing to catch up. Medtronic, based in Minneapolis, has presented its application for a consumer model of its Lifepak unit and hopes for approval in months. Cardiac Science of Irvine, Calif., said it hoped to submit studies to the F.D.A. for the consumer version of its Powerheart this spring and to gain approval well before year's end.  "People would like to see a journal study showing how placement in the home affects survival rates," Mr. Cohen, the research analyst, said. "But if they got the home defibrillator down to $700, it would sell incredibly well. It could become a baby boomer Father's Day gift and sell 500,000 units a year."  In the meantime, Philips is eagerly awaiting the first report of a life saved to put critics on the defensive. "I can't wait for that conversation," Ms. Katzman said.
It sounds compelling: be your household's own paramedic by wielding the electrodes that could restart a loved one's heart. But some doctors are skeptical.