Smoke poisoning is the most common fatal factor for indoor fires. A salesman claims that his company's new fire alarm has a built-in sound sensor that uniquely emits a sound when building materials are exposed to high temperatures. The alarm can accurately detect these sounds. It also sends out an alarm before the building materials actually catch fire, so that residents can escape before being trapped by smoke, so it can be a good replacement for traditional smoke alarms. Which of the following, if true, would most weaken the salesman's argument? ['The sound of many house building materials when they actually catch fire can be heard hundreds of meters away.', 'Many indoor fires start on mattresses and sofas, producing a lot of smoke without making a sound.', 'Data show that the use of smoke alarms has saved many lives.', 'Alarm systems with built-in sound sensors are much more expensive to install than traditional smoke alarm systems.']