It is one of the amazing inventions!
A simple device like a this is considered as an amazing gadget and it is also known as smoke alarm. It is safety equipment which detects smoke and issues an alarm to alert nearby people that potential fire is present. Smoke alarms automatically detect the presence of smoke. It proves its importance by saving many lives every year. It is important to put smoke alarms in the right places in your home. You should also test them regularly to make sure that they work properly.
If not checked in time fire could be disastrous hence it is considered mandatory to be installed in every home and office since it detects smoke from fire. Smoke alarms should be established on every floor of a house to ensure absolute safety. This fire fighting safety equipment has a smoke sensor to sense smoke and an electric buzzer to alert people about the break out of smoke.
Smoke rises, so most detectors are mounted on the ceiling or on a wall near the ceiling. Most smoke alarms are mounted away from kitchens to avoid the nuisance of false alarms. Most homes have at least one detector near any bedrooms to increase the chances of waking sleeping occupants, ideally in a hallway as well as in the bedroom itself.
It consists of two basic parts - a sensor to sense the smoke and a very loud electronic horn to wakeup people. This safety equipment needs regular maintenance and change of batteries.
            Because of mass production it is possible that these detectors are one which practically costs nothing. Studies have shown that smoke detectors save thousands of lives each year. In fact, it is internationally recommended that every home/Building must have one of it for each floor.
          Generally all smoke detectors consist of two basic parts:

1. A sensor to sense the smoke and
2.  A very loud electronic horn or speaker to wake people up.

   They can run off of a 9-volt battery or 120-volt (home supply).
There are two types of smoke alarms available commercially today.

1. photoelectric 
2. Ionization

                Both ionization and photoelectric detectors are the most effective smoke sensors. Ionization detectors respond faster as compared to flaming fires with smaller combustion particles. Photoelectric detectors respond more quickly to fire. The photoelectric detector uses an optical beam to search for smoke.
            In either type of smoke detector, steam or high humidity can lead to condensation on the circuit board and sensor, causing the alarm to sound. Ionization type of detectors is less expensive than photoelectric detectors. Some users purposely disable them because ionization detector is more likely to sound an alarm from normal cooking due to its sensitivity to minute smoke particles. However, ionization detectors have a degree of built-in security not inherent to photoelectric detectors. When the battery starts to fail in an ionization detector, the ion current falls and the alarm sounds, warning that it is time to change the battery before the smoke detector becomes ineffective. Back-up batteries may be used for photoelectric detectors.