2. Smoke detectors are made with different kinds of sensors that detect excessive smoke when it is present and gives out the alarm, or triggers the automatic fire control system. It is best that homeowners are able to see the difference among these different types and see how they work, before deciding on which ones to buy and install in the house. The type of sensor installed in a smoke detector may also dictate the price range, since there are sensors that have more expensive components than those of the other types. Among the types of sensors presently used by several manufacturers of smoke detectors are the ionization type, the optic sensor – also called photo electric sensor, the air sampling sensor, and combination type sensors. A smoke detector with an ionization type sensor uses what is called radio isotopes that produce ionization in the air. The process is quite technical, but what this type of detector contains is ionized air molecules in a chamber inside the device. The ionized air carries electrical current and maintains that current, until something disrupts the air molecules. When the air molecules are disrupted, usually by smoke, the current drops, and an electrical circuit sound the alarm. Ionization smoke detectors are said to be cheaper to manufacture, but the downside is that they are prone to false alarms. They sound the alarm at the slightest degree of disruption in the ionized air, even from ordinary smoke in the kitchen.