Smoke detectors have greatly improved residential life safety by quickly detecting and altering building occupants to the harmful effects of fire. Smoke and toxic gases are the leading killers. Smoke detectors are hard or permanently wired, battery operated, or a combination of hard wiring with a battery backup. Smoke detectors work primarily on two principles: ionization and photoelectric. Ionization detectors use a radioactive element that emits ions into the chamber. The positive and negative ions are measured on an electrically charged electrode. When smoke enters the chamber, the flow of ions to the electrode changes and an alarm is activated. Photoelectric detectors use two different methods to detect the smoke of a fire and can be spot or line detectors. The first is the light obscuration detector, which has a light beam aimed at a light sensor. When the smoke particles obscure or block the light beam, the light sensor notes the loss of light and activates the alarm. The light scattering detector operates by having a light beam aimed at the end of the chamber with a light sensor in an angled-off chamber.