Siren is a device that produces loud noise. They are the means communication. Sirens can be seen in emergency vehicles such as police cars, ambulances and fire trucks.
Generally, sirens are used as indication or warning. There are different circuits to produce different sirens. The word siren first originated in Greek mythology and was also later used to refer to mermaids. Language and literature have used the word siren as indicative of dangerous temptations. The siren as we understand today is not something dangerous, but is generally a warning signal either to stop or proceed, based upon who has used it. So, though the siren is in itself not dangerous, ignoring a siren, especially a police siren, can have dangerous consequences. The two basic types of sirens are pneumatic sirens and electronic sirens. All conventional sirens were pneumatic sirens and its energy requirements were much more compared to present day electronic sirens. Pneumatic sirens are also known as mechanical sirens. In electronic sirens different types of sounds are synthesized with the combined action of sound modulators, oscillators, and amplifiers. A siren today is mostly an electronic siren though some emergency vehicles may be fitted with both a pneumatic siren and an electronic siren