Siren FAQ Tool

Humans can hear in the range of 20 to 20,000 kHZ, but dogs can up to 45,000 kHZ. Ambulance sirens produce sounds from 10 to 40,000 kHZ, which is heard by dogs and in response they bark or growl.

These sirens are intended to introduce a wide sound spectrum to alert both people and animals of the presence of an emergency vehicle so that they can get out of the way fast.

This is also the reason why there is no spoken words in the ambulance siren, since animals, young children and people who do not understand the language can still be notified of an oncoming ambulance.

Ambulance sirens produce sounds from 10 to 40,000 kHZ which is beyond the usual 20 to 20,000 kHZ of humans, and can be as loud as 140 decibels.

To give you a comparison, a plane takeoff is 130 decibels and a construction concrete drill is at 110 decibels.

The siren sound is produced in increasing volume (louder and louder) and when the max volume is reached at 140db, then the volume will slowly drop to 20db.

The average volume of the siren is 80 decibels.

The loudness range of the siren is 20 to 140 decibels.

The sounds have different tones because ambulances will use a quicker tone to tell the people around of the urgency of the situation.

The different sounds have different meanings.

If there is a heart attack patient, the ambulance driver will likely use the quick siren to nudge traffic out of the way, whereas a bleeding from the shoulder patient will need a regular siren sound.

Should the ambulance siren sound change, it shows that the situation in the ambulance has also changed.

• If the sound speeds up, then the patient turned more critical.
• If the sound slows down, then the patient could have improved.
• If the sound is turned off, then the medical case could have been cancelled or the patient may have passed away.

Sirens are switched off if the ambulance responding to a case has its case cancelled. The situation may have been a prank call or the patient may have taken a taxi to the hospital.

Sirens are also not needed if the patient in the ambulance has been declared dead by the paramedic. In such cases, resuscitation and CPR has stopped. The ambulance will still proceed to the hospital to handover the patient, but without any rush and without the siren on.

It is a conscious decision for the ambulance to turn off the siren – even though the siren is available, the crew will still use its discretion to off the siren.

Ambulances have a speaker mounted externally. The speaker is usually front facing to alert drivers blocking its way. Smaller extra speakers may face the other directions, but they are usually less loud.

Ambulances also have a control panel which have 2 knobs.

• The first knob adjusts the volume. If the volume is turned to zero, the siren is switched on. The loudest the sound can go is 140 decibels.
• The second knob changes the siren sound. There are different tones. A faster one is used for very urgent or very critical cases. A regular tone is used for all other situations. There is also a speak-through option which allows the driver to use the microphone and speak through the mounted ambulance speaker.

If the siren sounds irregular, the ambulance may be switching between the tones as another form of using the horn. (The van’s horn may be less loud, so using a irregular switching siren sound can raise more alert to other road users and make them get out of the way.)

Another reason could be that the siren is malfunctioning. A tell-tale sign of a faulty siren is loud static noises. In those cases, the siren was not intended for use – it could be the ambulance medic troubleshooting its vehicle or a technician performing some servicing.

Ambulances are considerate when operating in residential areas. At night, most people are sleeping. Loud sirens will disturb the quiet restful sleep and increase complaint rates against the ambulance service, so ambulances will choose to drive without sirens at night.

In addition, there is little to no traffic at night. So there is no need to use the loud sirens to get drivers out of the ambulance’s way.

Ambulances use their sirens while getting to a case (responding to incident) and getting to a hospital (evacuation from incident).

Sirens are used to clear traffic and ensure that there is timely response when getting from location to location. Sirens also have different tones to signify urgency and criticality, and these siren tone-sounds are used based on the situation. The medics will consider on a case-by-case basis, and they have the sole discretion to use the siren for emergencies.

Although laws and rules patrolling the use of sirens are non-existent, ambulances form part of the public service and the employees face punishment if found that improper usage of the sirens had happened during their working shifts. The public also has the right to submit a complaint and the ambulance’s management may launch an investigation that can turn into tomorrow’s big news headline.

Since deaf drivers cannot hear, ambulance relies on their blinkers (flashing lights) to catch attention. The blinking lights pulsate up to 6,000 lumens.

For comparison, an orange flame in a lantern is 900 lumens. A car’s high-beam headlights reach up to 4000 lumens. And a helicopter’s searchlight is 60,000 lumens if pointed at your eyes.