­Smoke detectors are one of those amazing inventions that, because of mass production, cost practically nothing. You can get a smoke detector for as little as $7. And while they cost very little, smoke d­etectors save thousands of lives each year. In fact,it is recommended that every home have one smoke detector per floor.

All smoke detectors consist of two basic parts: a sensor to sense the smoke and a very loud electronic horn to wake people up. Smoke detectors can run off of a 9-volt battery or 120-volt house current.

In this article, we will examine the two most common types of smoke detectors used today: photoelectric detectors and ionization detectors. And, we'll also take a look inside an ionization detector.

Let's start with photoelectric detectors.

­

­