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The Two Main Types of Audible Alarms

You may not realize it, but many of the devices that you use on a regular basis are equipped with audible alarm devices. When leftover vegetables are done heating in the microwave, a small series of beeping noises lets you know that they’re ready. When there is smoke in your home, your smoke alarm lets out a piercing alert noise. When you leave the keys in your car’s ignition, a  beeping alert allows you to remember to remove them. However, not all of these alarm devices are the same. There are two main types of audible alarms, each of which have different properties. Here is a quick guide to the two main audible alarm types.

Why Does it Matter?

Many types of audible alarms are designed to serve a specific purpose. Some of these functions are for ‘reminders’ (such as leaving a car door open), while others are alerts for dangerous situations (such as the triggering of a glass-break burglar alarm). Audible alarms are extremely important for the function, safety and security of our everyday life. By understanding the different properties and limitations of audible alarms, you have the ability to choose the best type of alarm that will fit your specific needs.

The two main types of audible alarms are:

Electromagnetic Alarm
This type of audible alarm usually produces an alarm by activating a metal diaphragm with an electromagnet. This type of alarm has several advantages, the most prominent being the compact nature of its design. An electromagnetic alarm can be manufactured to produce from 100 Hz to 2,700 Hz. However, this type of alarm design usually uses a significant amount of power, and will incur a lot of mechanical wear. Another drawback is that it may have a low sound output.

Piezoelectric Alarm
This type of alarm is able to avoid using electro-mechanical contacts by using a different type of design. A piezoelectric transducer consists of ceramic (which has been appropriately polarized) that is directly connected to a disc of metal. Most piezoelectric alarms are able to produce sounds ranging from 1 kHz to 4.5 kHz. The advantages of this design include low consumption of power, little or no electrical ‘noise’, a very clear audible alarm sound, and very low mechanical wear on the alarm’s components.

Note: In reference to the second type of alarm, “piezoelectric” describes the properties of some materials to generate an electrical field when they are subjected to mechanical stress. This electrical field is generated in relation to a change in polarization within the specific material. In reference to a piezoelectric alarm, this material is usually ceramic.

Why Frequency Matters

The human ear is only able to process a limited range of sound frequencies. Frequency is measured in ‘Hertz’, by figuring out how many pressure variations a specific sound has per second. Most people are able to hear frequencies from 20 Hz to 20,000 Hz, though this may vary depending on several factors. For example, as a person ages, they may lose their ability to hear higher-frequency sounds, making a high-frequency audible alarm useless.

Here is an example of the typical range of frequencies for audible alarms:

Low: 1 – 2 kHz
Medium: 2 – 3.5 kHz
High: 3.5 – 4.5 kHz

Most people are especially sensitive to sounds that range from 2 kHz (2,000 Hz) to 5 kHz (5,000 Hz).

This is a general chart which shows the relationship between Decibels and Frequency.