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Get to Know the Alarms and Sirens

Author: Tanssion Date: 2023-08-31 Hits: 0

Ⅰ. What is a alarm?
Ⅱ. How many parts does the alarm device consist of?
Ⅲ. How does the infrared alarm work?
Ⅳ. The main functions of the alarm
Ⅴ. What are the commonly used alarms?
Ⅵ. Advantages and disadvantages of alarms
Ⅶ. What is the difference between a buzzer and an alarm?
Ⅷ. Overview of air defense siren

Ⅰ. What is a alarm?

An alarm is an electronic product that uses sound, light, air pressure, etc. to remind or warn us that we should take certain actions to prevent the consequences of an event. Alarms are divided into mechanical alarms and electronic alarms. With the advancement of science and technology, mechanical alarms are increasingly replaced by advanced electronic alarms. It is often used in fields such as system failure, security, transportation, medical rescue, emergency disaster relief, induction detection, etc., such as door sensors and gas induction alarms.

Ⅱ. How many parts does the alarm device consist of?

The alarm device consists of the following three main parts.

1. Control device

The control device is the hub of the alarm system and is divided into two types: wired control and wireless control. Wired control devices are connected through physical lines, and the transmission signal is more stable and reliable, but the wiring may affect the indoor appearance. Wireless control equipment does not require wiring and can be flexibly configured, but we need to pay attention to signal interference issues.

2. Power supply system

The power supply system provides electric energy for alarm equipment and is divided into two types: mains power supply and self-power supply. Mains power supply refers to obtaining electric energy directly from the mains, which is stable and reliable. Self-powering uses other energy sources, such as solar energy, wind energy, etc., and does not require wiring.

3. Siren

The siren is the part that makes the alarm sound, and is divided into two types: motor type and electroacoustic type. Motor-type sirens are driven by an electric motor and produce sound through mechanical components. The electroacoustic alarm consists of a host function and a speaker, and generates sound through electronic devices. Both types of alarms have their own advantages and disadvantages, and we should choose according to actual needs.

Ⅲ. How does the infrared alarm work?

The infrared transmitter emits a modulated infrared beam by driving an infrared light-emitting diode. We place an infrared receiver at a certain distance from the infrared transmitter. The infrared receiver receives the infrared radiation energy discovered by the transmitter through a phototransistor and converts it into an electrical signal through photoelectric conversion. This electrical signal is sent to the alarm controller circuit after appropriate processing.

The optical systems placed at the receiving and transmitting ends generally use optical lenses. It functions to focus the infrared beam into a thinner parallel beam so that the energy of the infrared light can be transmitted concentratedly. Infrared light is in the spectrum range that is invisible to the human eye. If someone passes through this invisible blockade, the infrared beam will be completely or partially blocked. The intensity of the electrical signal output by the receiving end will change accordingly, thereby starting the alarm controller to issue an alarm signal. Infrared through-beam alarms are characterized by very high detection reliability and are suitable for places such as high-voltage fences, highways, urban protection nets, bank counters, etc. to prevent intrusion.

Ⅳ. The main functions of the alarm

1. Help: When an emergency occurs at home, we can send a help signal to the outside world through the alarm to get help in time.

2. Prevent flammable gas poisoning: The alarm can detect the leakage of gas, liquefied petroleum gas, natural gas and other gases and issue an alarm in time to avoid poisoning accidents caused by gas leakage.

3. Fire alarm: The alarm can detect indoor smoke in time through the smoke detector and issue a fire alarm in the event of a fire, reminding users to take emergency measures in a timely manner, such as opening a fire extinguisher or evacuating.

4. Anti-theft alarm: When an illegal intruder enters, the alarm will immediately send out an alarm signal. It reminds the user through a high-decibel speaker or a connected alarm speaker, and at the same time sends an alarm signal to the outside world so that timely countermeasures can be taken.

Ⅴ. What are the commonly used alarms?

1. According to the sound pressure of the sound signal

(1) Small siren

The sound pressure level is below 40 decibels.

(2) Medium-sized siren

Sound pressure levels range from 90 dB to 50 dB.

(3) Large siren

The sound pressure level is above 100 decibels.

2. According to energy conversion method

(1) Electric sound alarm

The electroacoustic alarm converts small audio signals into sound energy after power amplification, that is, electrical energy is converted into sound energy. It consists of alarm signal source, amplifier, speaker and other components. 

The working principle of this type of alarm: The indoor unit is equipped with a set of digital circuits. The audio circuit sends the sound source signal to the amplification circuit. After amplification, it is then sent to the high-power loudspeaker by the line to be distributed around. Compared with the former, the electric alarm has a loud sound and a relatively wide coverage area. However, it cannot sound when there is a power outage, and the circuit structure is complex and the construction and maintenance costs are high.

(2) Electric siren

An electric alarm uses an electric motor as the main component of the alarm, which converts mechanical energy into sound. The alarm drives the sounding wheel to run at high speed through the electric motor, and the general speed is around 2880r/min. When the motor drives the sounding wheel to rotate, air enters the sounding wheel from the side air inlet, and the absorbed air generates high speed and high pressure and is extruded simultaneously to the window of the fixed wheel to create resonance. The disadvantage of electric sirens is that they cannot sound when there is a power outage, and the coverage range is relatively small compared to electric sirens.

The electric alarm is composed of main components such as a base, a positioning base, a motor, a sounding wheel, a fixed wheel, a positioner and a stainless steel cover. It is divided into two types: discrete and horizontal electric alarms.


① Base: The bracket of the entire alarm.

② Positioning seat: The support for fixing the positioner.

③ Electric motor: It is the power of the alarm. It drives the ring wheel to rotate and play the role of sound.

④ Sounding wheel: The most important part of the alarm, it rotates at high speed during work to produce a sound source.

⑤ Fixed wheel: A part that matches the height of the ring wheel. It usually has about 10 pronunciation windows and the pronunciation window is equal to the pronunciation blade of the sound wheel.

⑥ Locator: It can automatically close the sound window when the sound wheel is not working or stopped to prevent mice, birds, spiders, airborne debris, etc. from entering the alarm and play a role in protecting the alarm.

⑦ Stainless steel cover: On the one hand, it amplifies sound after sound refraction; on the other hand, it protects the entire alarm and prevents rainwater from entering the alarm.

(3) Pneumatic alarm

It converts electrical energy into mechanical energy, mechanical energy into gas energy, and gas energy into sound energy.

(4) Hand-operated alarm

The hand-operated alarm is a supplementary device for issuing civil air defense warning signals. The volume of the alarm sound depends on how fast the handle is shaken. When used, it needs to manually shake the handle clockwise by hand. The ideal alarm effect can be achieved when the speed reaches 50-80 rpm.

The hand-operated alarm includes a handle, a gear speed-increasing mechanism, a clutch slider, a fixed wheel, a sounding wheel, a sound window cover, a gear box, and a box frame. The handle is connected to the driving shaft of the gear speed-increasing mechanism; the output shaft of the gear speed-increasing mechanism is connected to the clutch slider through a pin; the clutch slider is frictionally connected to the flange of the impeller.

The hand-operated alarm is driven by manually turning the rocker, which is accelerated step by step through the transmission of the gear box, and then drives the sounding wheel to run at high speed through the transmission block. During the high-speed operation of the sounding wheel, the absorbed air generates resonance caused by high-speed and high-pressure extrusion to the fixed window of the fixed wheel at the same time, thereby acting as an alarm. The sound level of the hand-cranked alarm depends on the speed of the hand-cranked alarm. Compared with the previous two types of sirens, this type of siren has the smallest sounding range and is not affected by electricity.

3. According to the conditions of use

(1) Lifting siren

It refers to a siren that is hidden underground at ordinary times and rises out of the ground to give an alarm when an alarm needs to be issued.

(2) Fixed siren

It refers to the alarm installed in a fixed location.

(3) Mobile siren

It refers to a siren mounted on a motor vehicle or otherwise used in motion.

Ⅵ. Advantages and disadvantages of alarms

1. Advantages

(1) The alarm can be connected to various sensors to detect various environmental changes. As long as the change reaches a certain value, the alarm signal sent out can achieve the alarm function in time and accurately.

(2) The alarm can detect environmental changes in time, achieve the function of alarm reminder, and send the alarm signal to the alarm contact in time.

2. Disadvantages

(1) The detection range of the alarm is generally small, and it may not be able to detect long-distance environmental changes.

(2) The installation and maintenance of the alarm are complicated, which may cause the alarm signal to fail to be sent out in time.

Ⅶ. What is the difference between a buzzer and an alarm?

There are many types of alarms, such as buzzers, electric bells, and electric whistles are all alarms. The buzzer is an essential part of the alarm. Like the anti-theft and anti-theft alarm, it alarms through the high-decibel speaker of the host or the connected alarm speaker, and sends an alarm signal to the outside at the same time. The alarm for fire protection is to detect indoor smoke in time through smoke detectors and send out a fire alarm. These alarm functions are realized by using the buzzer sound principle.

Buzzers are used in various alarm devices, such as household alarms, commercial alarms, fire alarms, temperature alarms, etc. It has the characteristics of small size, high sensitivity, low power consumption, good reliability and low cost.

But buzzers and sirens are functionally different. Buzzers are mainly used to send out simple sound signals to prompt or display certain status or information. The function of the alarm is more complicated. It needs to convert physical quantities into electrical signals through sensors, and combine them with the processor for analysis and processing, and finally send warning signals to users in various ways such as sound and light to ensure the safety of people and property. For example, in fire alarm systems, buzzers are used as a means of preliminary warning, while smoke sensors are one of the devices that trigger various fire prevention measures after detecting flames.

Ⅷ. Overview of air defense siren

Air defense warnings are an important part of urban air defense work. It is used for disaster forecasting and emergency notification in case of emergencies in peacetime, and for civil air defense in wartime. It is the basic means for people's governments at all levels to implement civil air defense command and organize personnel evacuation. It has two main functions: one is to issue and transmit air raid warning signals to urban residents; the other is to provide guarantee for the people's government to organize and implement anti-air raid command.

1. Selection of air defense siren address

The installation of air defense alarm equipment is closely related to the construction of civil air defense network, which has specific requirements for the installation and location selection of alarm facilities. Scientific site selection can not only improve warning coverage, but also reflect the role and status of air defense warnings in both peacetime and wartime. When selecting the address of the air defense siren, the following points should be noted:

(1) The overall layout of the location is reasonable.

(2) If the selected location is an independent room, the room size cannot be less than 10 square meters.

(3) Select the appropriate layout building height.

(4) The selected placement location can be properly managed.

(5) The installation of equipment requires attention to the configuration of the power supply, and we need to reinforce the basic components of the installation.

2. Types of air defense alarms

(1) Advance warning

Early warning is the warning issued when there is a warning before the enemy attacks our side. The alarm sounds for 36 seconds, stops for 24 seconds, repeats 3 times as a cycle, and the total time is 3 minutes. At this time, citizens should immediately stop all work, turn off the power, turn off the gas, extinguish the fire, close the doors and windows, carry daily necessities and protective equipment, and quickly evacuate to the nearby underground air defense shelter. This is to ensure the safety of citizens' lives and property, and to deal with possible wars and attacks. In an emergency, citizens need to remain calm and evacuate to a safe place in an orderly manner according to the emergency plan.

(2) Air raid warning

The air raid warning is issued when the enemy is about to attack our side. During the sounding of the alarm, people should seek safe places to take refuge as soon as possible, such as underground air defense shelters, civil air defense projects, air-raid shelters, etc. But sometimes people may not be able to enter these shelters in time. At this time, they should use the terrain and features to hide nearby, lie on the ground and hold their heads in their hands to protect their head and life safety as much as possible. The air raid sirens are issued regularly, with each cycle sounding for 6 seconds and stopping for 6 seconds, repeating 15 times as a cycle, which lasts up to 3 minutes.

(3) Clear the alarm

All-clears are issued when air strikes or the fighting situation temporarily eases. Once the all-clear alarm sounds, citizens can safely walk out of the underground air-raid shelters and resume normal life and work.


Frequently Asked Questions

1、What is the use of alarm siren?
A siren alarm is one of the most basic home security products out there, providing effective protection for your home at a reasonable price. Siren alarm systems work by generating a loud, piercing siren sound when they're triggered by intruders in and around your home.
2、How many decibels is an alarm siren?
A siren must be at least 85 decibels (dB) to meet Nationally Recognized Industry Standards. Even though industry standards require a siren to be at least 85 dB, this still might not be loud enough for certain applications.
3、How does a mechanical siren work?
Mechanical sirens blow air through a slotted disk or rotor. The cyclic waves of air pressure are the physical form of sound. In many sirens, a centrifugal blower and rotor are integrated into a single piece of material, spun by an electric motor.
4、What is a defender siren?
The SA-361 Defender Siren is designed to work with a single 100-watt siren speaker and includes a mounting bracket, external fusing, short circuit, high voltage and reverse polarity protection systems and an output indicator light for diagnostic purposes.

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