CLEVELAND -- A 5 On Your Side investigation has discovered a potentially deadly problem with the most popular type of smoke detectors, reported NewsChannel5's chief investigator Duane Pohlman.

Experts, studies and firefighters all agree that having at least one smoke detector in every room is important for every home. Most people don't know that there are two kinds of smoke detectors, and one can take a little longer to go off.

Pohlman reported most stores sell 2 kinds of smoke detectors. One is ionization and the other is photoelectric. Photoelectric detectors sense the light that gets scattered when the smoke thickens. Ionization detectors are designed with a chamber that senses positive electrons. When the fire changes those electrons, that triggers the alarm.

Nine out of 10 homes rely on ionization smoke detectors alone.

5 On Your Side conducted an unscientific test to compare the response time between the two types of detectors. Using a simple aquarium, we buried a soldering iron into a chunk of foam to simulate the kind of smoky fire that can be deadly. 5 On Your Side also put a carbon monoxide monitor inside the tank to check the levels of deadly toxins that can build up as the smoke fills the tank.

First, 5 On Your Side tested the ionization smoke detector. Within one minute of placing the soldering iron into the chunk of foam, it started to smoke. Two minutes later, so much smoke filled the aquarium we couldn't see the detector at all. After another 4 minutes and 20 seconds, the smoke got thicker, but the alarm didn't go off. But the carbon monoxide monitor registered 260 parts per million. That amount is enough to cause headaches.

A few seconds later, the ionization detector still hadn't gone off. The carbon monoxide monitor registered 418 parts per million, which is enough to cause nausea. Five and a half minutes into the test, the carbon monoxide detector registered 831 parts per million, a very dangerous level that causes dizziness and set off the carbon monoxide monitor. Even so, the ionization smoke detector did not go off until 10 minutes and 18 seconds after the first tendrils of smoke started filling the tank.

Next, 5 On Your Side tested the photoelectric smoke detector. It went off 4 minutes and 38 seconds after the smoke started filling the tank. Experts said that's still a long time, but it's more than twice as fast as the ionization type. 5 On Your Side conducted the same test on a dual detector that contains both ionization and photoelectric sensors. That dual detector went off in 1 minute and 16 seconds. That's nine minutes faster than the ionization detector, and according to experts, that's enough time to potentially save a life.

These non-scientific tests didn't come as a surprise to fire experts. 5 On Your Side showed the tests to Ohio Fire Marshal Michael P. Bell. He said, "We know that with a slow, smoldering fire, the photoelectric will be a better choice."

Most smoke detector manufacturers agree. The fine print on many packages reads, "For maximum protection, you should use both types of smoke detectors."

In the latest, most comprehensive test of smoke detectors, the National Institute of Standards and Technologies found each smoke detector works well in most conditions. But when it comes to a smoldering chair, "the ionization alarms did not, however, provide positive available egress time in every test."

In other words, sometimes the ionization smoke detectors don't give people enough time to escape.

Be sure to watch Friday when Pohlman checks homes in the Cleveland area to see which kinds of smoke detectors most people are using and how best to protect your family.