Smoke usually moves up to the ceiling. Smoke alarm sensor detects fire by smoke. The smoke alarm sensor already detects the fire before you see the fire flame or smell the smoke. It works without stop: 24 hours daily and 365 days annually. Upon alarming, it makes screaming voice until the smoke disappears.

　　In real fire case, the smoke sensor works until it is burnt out.
There are two options on independent style smoke alarm sensors used in civil residence: one is ion sensor while the other is called photoelectrical sensor.

　　Ion sensor works by measuring the balance between positive ions and negative ions in the air. Within the sensor, there is a very small radiation substance which can sense the weak current generated in the moving air in the room. There is a chip in the PCB which can detect such current. When smoke particle enters the sensing room, it interrupts the balance between positive and negative electric charge as well as changes the current. The imbalance of positive and negative electric charge will increase when the smoke gradually grows. The buzzer will immediately blow when this imbalance increases to a limitation.

　　Fire misreporting is a serious issue. When fire case does not actually happen but the smoke alarm sensor continuously makes alarming sounds thus you may remove the sensor resulting in non-alarming when fire accident does in fact happen.

　　The fire misreporting causes as follows: a. cooking b. influence factors from vapor or humid air c. cigarette smoke d. electrical power e. dust

　　Many fire misreporting from cooking smoke are sounded from ion alarming sensor because this kind of sensor is relatively sensitive to very small smoke particle which is even unable to be seen by human eyes while smoke particle from cooking smoke at high temperature can not be seen by human eyes.

　　There are two basic solutions to this problem. Firstly it is to move the position of sensor. Place the sensor away from cooking area to make the smoke less when it reaches the alarm sensor thus decreasing fire misreporting. But this method does not always work especially when moving air brings the cooking smoke to the sensor and it also can make fire misreporting. Therefore it is definitely required that the air moving direction must be made sure when the sensor is moved.

　　Secondly it is to replace an alternative sensor: A. to buy an ion sensor with silent button. This sensor sounds in every 15 minutes when the button is pressed thus making enough time to remove the cooking smoke. B. to buy a photoelectrical sensor which is not so sensitive to smoke particle and does not make fire misreporting.

　　Vapor or humid air can concentrate on the sensor and PCB. The sensor makes alarming sound if the concentrated vapor reaches a larger quantity.
Solutions: to place the sensor relatively far away from a steamy or humid area. For instance, bathroom is not considered to be the right position for installing sensor. However, the sensor could usually work normally but it is currently sensitive to steamy and humid air, this problem may be from the aged sensor.

　　Relatively old sensor would be even sensitive to steamy and humid air. Therefore fire misreporting may also happen due to the aged sensor. It is time to replace it with a new one.

　　In general, smoke alarm sensor is not sensitive to cigarette smoke unless the smoke is too heavy. For instance, that many cigarette smokers smoke at the same in a room can make the sensor sound alarming. If the sensor is too old, it can alarm even the smoke density is very low. On the contrary, in this case, we can determine and judge if the sensor is already too old.

　　Before the battery Is nearly used up the sensor makes chirring sounds ( sensor of different models makes different sounds but all has pre-alarming function because of insufficient power). This is also considered a fire misreporting to some people. But it is very easy to judge on it because it is a single but short sound. Besides, it sounds once in about one minute. If your sensor makes such sound intermittently, you are recommended to replace the battery to see if this problem can be solved.

　　If the sensor makes alarming sounds continuously, then it is considered that there is too much dust accumulated in the sensor and it is time to replace it or clean it. Upon cleaning the sensor, it is recommended that the vacuum cleaner end is placed towards the mouth area of sensor and vacuum the dust one by one, in this way the dust accumulated on the sensor can be completely removed.

（3）Is smoke alarm sensor applied working？

　　As the smoke alarm sensor users increase, the death quantity due to residence fire case continuously decreases. The report by the national fire association in USA indicates that in case the house with recommended qty of smoke alarm sensor is on fire, the possibility of successfully escaping from the fire for the family members is 50% higher than those houses without alarm installation.

（4）Is my smoke alarm sensor to be replaced ?

　　If the use of smoke alarm sensor is nearly 5 years, it is time to replace it. Some people think their smoke alarm sensor work only when there is smoke but in fact they do work all the time, continuously detecting the change of air. For example, ion smoke sensor circulates for 1.75 million times in 5 years. Photoelectrical smoke alarm sensor works 24 hours daily to detect the smoke particle in the air.

　　Just as other electric items, smoke alarm sensor wastes away as time goes. A smoke sensor after 5 year use is loosing its fire-detecting function and performance capability, thus it is better to change it.

（5）How many smoke alarm sensors are required to be installed in an ordinary　house？

　　Ordinary family needs to install at least one set of smoke alarm sensor. Actual quantity is decided by two factors—the numbers of floor and bedroom.

　　The following suggestion is based on the house fire alarming standard made by National Fire Association in USA:

　　a. It is required to install one set of sensor in every bedroom according to the standard.

　　b.It is required to install one set of sensor in a place outside bedroom where alarming can be heard.

　　c.It is required to install at least one set of sensor in one floor.

　　It is quite necessary to install one set of sensor in every bedroom. There are many fire cases occurred in bedroom. The sensor can make better alarming if it is installed more close to the place where fire accidents occurs.

　　The installation of smoke alarm sensor outside bedroom is to remind family members that there is fire outside bedroom. If the bedrooms are positioned independently, it is required to install one set of sensor in each bedroom.

　　If a house is too big, it is required to install more than one set of sensor in each floor.

　　Smoke alarm sensor detects fire by smoke. It more quickly responds to the fire when it is more closely installed to the firing place. In this case, to install several more smoke alarm sensors makes you feel safer.

（6）Which parts of a house does not need installation of smoke alarm sensor？

　　It is not recommended to use alarm at those places where it is extremely hot or cold or there is too much dust as well as roof and alike. The manual made by manufacturer tells you where the alarm is most applicable.

　　Smoke alarm sensor is not applicable to garage due to two reasons: one is that garage is not much influenced by outside temperature thus the sensor would deviate the temperature sensing range of the alarm while the other is that emitted gas from vehicle at garage would bring misreporting of fire.

　　Another place which is not recommended to install alarm is kitchen. If it is installed too close to the cooker, it would result in misreporting. NFPA72 requires that a photoelectrical device or silent button should be installed at the same time when smoke alarm sensor in installed within 20 feet to cooker.

（7）Which smoke alarm sensor is better？

　　Every alarm sensor meets all testing standards but each of them has its own advantages.Ion alarm sensor is more quickly sensitive to smoke particle. Visible fire ( such as burning paper) and quickly burning big fire, ion alarm sensor makes alarming earlier than photoelectrical one because there is more smoke particle in the air.

　　However, photoelectrical alarm sensor is more quickly sensitive to bigger smoke particle. When there is invisible fire (such as cigarette ends catches fire in sofa), the smoke particles in the air is bigger, then photoelectrical alarm sensor makes alarming earlier than ion alarm sensor.

　　The alarming time space is not big for these two kinds of alarm sensors. However, fire moves very quickly, thus time is critically important to save a life.

（8）What kinds of method can I use for testing the smoke alarm sensor？

　　Every smoke alarm sensor has one testing button when it is made. Manufacturer suggests all users test the alarm by themselves at least once a month.

　　This testing method is not recommended because the burning substance for making smoke can really make fire happen. This is very dangerous as there is usually a lot of flammable materials in bedroom and visible fire can easily bring fire accident. It is the best way to use button.

（10）Is it important to regularly clean the sensor？

　　Regularly cleaning alarm is very important. There is some small silting shape hiding substance near the sensing center to prevent small bugs coming from outside from entering the sensing center. But dust can accumulate around the hiding substances delaying the air movement. Cleaning alarm is an easy job. It is to use vacuum cleaner to vacuum the dust outside the unit and it is recommended at least once for a year. That is it.