The different types of Audible Warning Signals

The different types of Audible Warning Signals

When choosing an audible warning signal for industrial purposes, there are some aspects you need to consider before choosing the correct signal.

Firstly, you need to consider what type of audible warning signal you require from a range of:

Electronic Sounders

In today’s world of technology, an electronic sounder is the most versatile product to use as this can be programmed to offer multiple tones and can be volume adjustable, making them suitable for almost every requirement. – – Sirens.

Sirens are a motor-powered device producing a unique sound due to its internal impeller.


Bells are suitable for daily signalling use that produces medium db output. Most commonly found in schools and workplaces to alert for lunch breaks.

Air Horns

Air horns are a good option for industrial & marine areas and hazardous areas. It is a non-electrical device with a high db output and low frequency, making it ideal for noisy environments.


This is an electro-mechanical type of warning signal in a robust housing. They produce medium-high db output with a low sound frequency


Hooters are a motor-powered warning device with a horn. It has a high db output with low sound frequency, ideal for indoor and outdoor use.

You now need to take into consideration the sound level and frequency rating of your chosen alarm – this needs to be heard instantly and distinctly above any other noise in the area.

Next you need to consider the power consumption, electrical supply and IP rating of your chosen alarm and check with your engineer this will be suitable for your application.

Lastly you need to ensure you choose a quality product that will stand the test of time so to speak. By purchasing a quality product to begin with, it will save you time and money in the long run in maintenance, especially if the alarm is located in a hard to reach area.

Sounders & Sirens

Sounders & Sirens

Sounders and sirens are used to attract attention particularly when an immediate response is required. To alert a person, it is recommended that a sounder or siren reaches between 5 and 15 dB(A) louder than the background noise of the given area.

There are several things to consider before selecting a sounder or a siren:

  • The sound pressure level achieved (quoted as decibel or dB(A).
  • The distance it must be audible over.
  • The frequency quoted in Hz.
  • The background noise of the area it will be installed in.
  • The duration of each use – duty cycle or prolonged use.
  • Ensuring the tone of the sounder or siren does not sound similar to any machinery etc in the same area.

To enable an easy comparison, the dB(A) stated for a sounder or siren is usually measured at a distance of 1m. When the distance is doubled the dB(A) is to drop by 6. This is why it is important to know not only the dB(A) of the sounder or siren is capable of, but also the distance away from the intended area it will be placed.

Using our IAS-E sounder and MDS-2 siren as an example of this:

DistanceIAS-E SounderMDS-2 Siren
1m110 dB(A)114 dB(A)
2m104 dB(A)108 dB(A)
4m98 dB(A)102 dB(A)
16m86 dB(A)90 dB(A)
128m68 dB(A)72 dB(A)
256m62 dB(A)66 dB(A)
512m56 dB(A)60 dB(A)
1024mx54 dB(A)

As you can see from the above, when choosing a sounder or siren, louder is always better. It is worth noting however that studies have found that is it possible to distinguish a sound that is up to 10 dB below ambient as long as there is sufficient frequency differential.

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Motor Driven Sirens

Motor Driven Sirens

Motor driven sirens are a typical style of an audible signal. They work by the motor driving a bladed impeller, pulling in air and pushing it back out through vents to produce a whirring sound – similar to an air raid siren. These units are commonly used in remote areas where a distinct noise it required to warn of an emergency.

Motor driven sirens usually have a duty cycle; for example 5 mins on and 10 mins off, so be sure to check this suits your application before using one.

As with all audible signals, these sirens have many pro’s and con’s:


 – Tend to be lower priced due to a simpler design.

– Lower frequency which travels better through and around object.

– Good to use in remote areas or in an area where electronic tones are used for fire alarms, and a siren is required to warn of something else.


– Is only single tone and has no volume control.

–  High current draw and low efficiency.

– Lower IP rating due to the exposed blades which can get blocked with dust and debris.

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Sounders & Sirens

Audible Warning Signals

Your bedside alarm clock may be far from your best friend, but it serves a purpose – to wake you up. This is a very simple example of an audible signal – audible warning signals and audible alarms are on a completely different scale, which is why it’s important to know the different types of audible warning signals available.

Types of Audible Warning Signals

Audible warning signals are available in various forms:

  1. Air horns
  2. Electronic Sounders
  3. Bells
  4. Hooters
  5. Buzzers
  6. Sirens


Sound Level and Frequency Rating

The sound level of an Audible Alarm depends upon the decision of the designer. Sound level is the amplitude of air pressure produced by the alarm. Moreover, frequency rating is also an important characteristic to consider in audible alarms. In music, frequency rating is known to be the pitch. It is the number of pressure variations per seconds measured in Hz.

Power Consumption

Power consumption has become an important issue when it comes to product design. Audible alarms need around ten mA to more than 80 mA in order for it to operate.

Quality of Construction

Of course, never forsake the quality of an audible alarm. In order to get the most effective alarm, check its construction.

Quality Testing

This audible alarm basic is important to guarantee that an audible alarm is really suitable. This can include the testing of the surge voltage, reverse voltage, water spray (IP Rating), shock / vibration, and so on.

Our range of Electronic Sounders:

IAS-C Series

114dB Multi-tone Electronic Sounder 85mm High x 94mm Dia.

  • – IP65
  • – 64 Tone combinations
  • – Maximum output 114dB(A)
  • – Internal volume control
  • – 10-30Vdc, 24Vac, 115-230Vac/dc and 45-65Vac/55-95Vdc models
  • – 2-wire connection with third-wire for alternate tone selection
  • – Compatible with full Series B and Series C ranges to provide a fully customised and integrated signalling solution
  • – Standard White ABS base and horn, optional Red base and horn available
  • – Suitable for BESA box mounting
  • – Side and Base entry


IAS-E Series

114dB Multi-tone Sounder 117mm High x 146 Dia.

  • – IP65 (Horn must not be mounted pointing upwards)
  • – 64 Tone combinations
  • – Maximum output 114dB(A)
  • – Internal volume control
  • – 12Vdc, 18-55Vdc, 15-40Vac, 115-230Vac/dc and 45-65Vac/55-95Vdc models
  • – 2-wire connection with third-wire/fourth-wire for alternate tone selections
  • – Standard White ABS base and Red horn, optional White or Black horns available.
  • – Suitable for BESA box mounting
  • – Side and Base entry



IAS-T Series

114dB Multi-tone Sounder 171mm High, 150mm x 150mm Base

  • – IP66 (Horn must not be mounted pointing upwards)
  • – 64 Tone combinations
  • – Maximum output 114dB(A)
  • – Internal volume control
  • – 12Vdc, 18-55Vdc, 15-40Vac, 115-230Vac/dc and 45-65Vac/55-95Vdc models
  • – 2-wire connection with third-wire/fourth-wire for alternate tone selections
  • – Compatible with full Series T, U and V ranges to provide a fully customised and integrated signalling solution
  • – Standard Black polycarbonate base and Red horn, optional White or Black horns available
  • – Side and Base entry




More information can be seen here:


Pneumatic & Electronic Sirens


Hearing is one of the most important senses a man can have. It allows a person to hear sounds through the mechanical waves that are transmitted and stimulates the hearing organs. Each of the Earth’s components and everything that is in it including plants, animals and humans can create sounds that are unique from each other. Man creates sounds through his voice, actions and in special instruments that are being used in music such as pianos, organs, guitars, violins, drums, bongos, cymbals and xylophones. These instruments are made in order to enjoy music. Music is a form of art with sound as a medium. It is a combination of musical notes, pitch and duration as its foundation. While music has a pleasing effect on the listener, noise on the other hand obstructs, garbles, and is unpleasant for a person to hear because of its irregular wave form, low frequency, and sudden changes in wave length. It is also an unwanted sound which is usually very loud and meaningless.alarm-system-icon-20

Although noise can be unpleasant to hear and unwanted by many people, it may prove very useful in some applications especially in audible warning signal devices, which attract people’s attention by sounding very loud sound signals. Last week, we discussed the different types of audible warning signal devices that are commonly used today. One of those devices is the siren which gives a loud warning signal to people around the area. And so this week, we will briefly discuss the two types of siren – the pneumatic siren and the electronic siren. We will also discuss in this article how those two sirens work, their uses, and in what applications they are being used.

Pneumatic Sirens  

Pneumatic sirens are typically aero phones or instruments that produces sound primarily by causing a body of air to vibrate and without the use of strings or membranes. It consists of a rotating disk with holes in it which are called chopper, siren disk or rotor. The materials between the rotor interrupts the flow of air from fixed holes on the outside of the unit which are called stator. The stator is the part which cuts off and reopens air as the rotating blades of the rotor move past the port holes of the stator which results in generating or producing a sound. As the rotor alternately preventing and allowing the air to flow, it results in alternating a compressed and rarefied air pressure. The pitch of the siren’s sound is a function of the speed of the rotor and the number of holes in the stator. A siren with only one row of ports is called a single tone siren. A siren with two rows of ports is known as a dual tone siren. You can also repeatedly close and open all of the stator ports that will create a pulse by placing a second stator over the main stator and attach a solenoid into it. If this is done while the siren is wailing rather than sounding a steady tone, it is called a pulse wail. By doing this separately over each row of ports on a dual tone siren, one can alternately sound each of the two tones back and forth which will create a tone known as Hi/Lo. If this is done while the siren is wailing, it is called a Hi/Lo wail. The ports can be opened and closed to send Morse code. This type of siren which can do both pulse and Morse code is known as a code siren. Pneumatic sirens consume large amounts of energy. And in order to reduce the energy consumption without losing sound volume, some designs of pneumatic sirens are boosted by forcing compressed air from a tank that can be refilled by a low powered compressor through the rotor.

In the United States, pneumatic sirens that are mounted in vehicles are sometimes referred to as mechanical or coaster sirens. Mechanical sirens powered by an electric motor are often called “electromechanical” because of its high current draw. Pneumatic sirens are usually being used with fire trucks, type IV ambulances, rescue-squad vehicles, and in other applications such as aviation and loading bays. Its distinct tone of urgency, high sound pressure level and square sound waves are remarkable for its effectiveness.

Electronic Sirens

Electronic sirens are made up of electronic circuits such as oscillators, modulators, and amplifiers to synthesize or produce a selected siren tone which is played through external speakers. They are basically high-performance sound signal electronic amplifiers just like those in home sound systems. However, these sirens work with substantially higher outputs and specific demands are placed on them in terms of desired extreme reliability and different methods of their control. Control infrastructure must also be reliable and usually two independent control channels are required. The loudspeakers for these amplifiers are placed in specially-designed sound baffles and they play the signals stored in the siren’s digital memory or signals fed to the siren from an external source such as a microphone, phone, radio station, common radio and television broadcasting, etc. Electronic sirens are increasingly used for mass warning systems due to their advantages of low energy consumption and low maintenance effort. Their modular construction offers individual structure and power stages possibilities. The first electronic siren that mimicked the sound of a mechanical siren was invented in 1965 by Motorola employees Ronald H. Chapman and Charles W. Stephens. Like pneumatic sirens, electronic sirens are also being used in aviation, loading bays, rescue-squad vehicles, and in emergency vehicles such as fire trucks and ambulances.

Noise can be compared to the idiom “two sides of a coin”. If we look at it, we’ll see that it has two sides, both of which bear different imagery. Noise can really be annoying and some may consider them as garbage or trash, but it has some benefits and uses if we look at it in a different way. When we say “two sides of a coin”, what we refer to is the fact that an issue might look very different when we flip it over and look at it from the other side. It is the same item, but it looks different, depending on your perspective.