06Sirens, horns and alarms

The short version: A modern emergency siren is a speaker playing a menu of synthesized tones - wail, yelp, hi-lo, phaser - chosen by the driver for the traffic in front of them. How loud it is depends on where you stand: a 1985 federal field study measured an ambulance siren at 122 dBA at 10 feet and 98-105 dBA at 100 feet. Countries do not agree on what a siren should sound like - German law allows a single two-tone horn as the warning tone - and fixed outdoor sirens, Japan's evening chimes and car alarms each follow their own rules.

What are the different siren sounds?

What you hear: a slow rise and fall, then a frantic fast warble as the vehicle reaches an intersection, sometimes two alternating notes or a blast of air horn.

Electronic sirens synthesize their tones and play them through external speakers mounted on the roof or behind the grille. The standard menu includes wail, yelp, pierce/priority/phaser, hi-lo, scan, air horn and a manual mode⁹⁵. Older mechanical sirens make the wail physically: a rotor spins up and slows down, and the pitch rises and falls with it. A mechanical hi-lo uses solenoids to switch air between two rows of ports⁹⁵.

Two-tone sirens often sound a minor third apart; some police sirens use a tritone⁹⁵.

The history runs from bells to a two-tone (duotone) air horn in the 1970s, which the electronic wail overtook in the 1980s, according to Wikipedia's account, which does not name the country but reads as US history⁹⁵. Some US fire apparatus still carry a mechanical siren, the Federal Signal Q2B, rated at 123 dB at 10 feet (weighting not stated)⁹⁵.

What is the police siren that makes my car shake?

What you hear: a deep, throbbing pulse under the regular siren, often felt through the floor or steering wheel before you notice it as a sound.

That is probably a Rumbler, a Federal Signal add-on developed in 2007 and tested by the New York Police Department that year as an "intersection clearing device"⁹⁶. It plays a low-frequency tone between 182 and 400 Hz alongside the standard siren⁹⁶. The manufacturer says the unit senses the primary siren tone and drops its frequency by 75%, claims "up to 10 dB more sound pressure inside civilian vehicles," and limits each activation to eight seconds before it shuts off automatically; it is rated at 80 W⁹⁷. Those performance figures are the maker's own claims.

By 2012 more than 100 US police departments had deployed it, according to the advocacy group Noise Off as reported by Wikipedia⁹⁶. The manufacturer's own product page warns that audible equipment can cause hearing damage and recommends hearing protection⁹⁷.

The logic is physics. Drivers in sealed, insulated cars with music on often miss a siren, and low frequencies pass through car bodies better than high ones. The Rumbler trades a sound you hear for a vibration you feel.

Why do sirens sound different in Europe?

What you hear: in a German city, a steady "ta-tu-ta-ta" alternating between two notes, with none of the American wail or yelp.

Because the law says so. In Germany, priority vehicles may use one emergency tone: the two-tone Martinshorn (formally the Folgetonhorn or Einsatzhorn), defined by the standard DIN 14610⁹⁸. The current edition of DIN 14610, "Sound warning devices for authorized emergency vehicles," is dated March 2022⁹⁹; a petitioner to the German parliament said the standard's origins go back to 1935⁹⁸. Emergency horns must also meet Technical Requirement No. 32, which references DIN 14610⁹⁸.

In 2022 that petition asked the Bundestag to allow US-style wail and yelp. The government's position, as summarized in the closing statement, cited a Federal Highway Research Institute (BASt) study that found no basis for changing the signals and said how far a siren carries depends mainly on the traffic situation⁹⁸. The petition was closed on March 14, 2024 as "partially met": yelp was introduced, but only as a stop signal for police and customs vehicles under section 55(3a) of the vehicle licensing regulations (StVZO), not as a general warning tone⁹⁸.

In the US, by contrast, an emergency vehicle can rotate through the full electronic menu described above⁹⁵. German-style pneumatic two-tone (hi-lo) units switch between a high and a low air horn and can reach about 125 dB, depending on the compressor and horns (distance not stated)⁹⁵.

In the UK, the two-tone horn behind the "nee-naw" goes back at least to the 1960s: the British Red Cross museum holds a set of Fiamm two-tone air horns, made between 1960 and 1970, that were fitted to an ambulance as its siren¹⁰⁰. UK law still names the device. The Road Vehicles (Construction and Use) Regulations 1986 bar any motor vehicle from being fitted with a bell, gong, siren or two-tone horn, with exceptions for fire, police and ambulance vehicles and a list of rescue and other services¹⁰¹.

How loud is an ambulance siren?

What you hear: painful at the curb, still loud a block away.

The best-documented US figure comes from a 1985 National Institute for Occupational Safety and Health (NIOSH) Health Hazard Evaluation, requested by the General Services Administration before it revised the federal ambulance specification. Outside the vehicle, NIOSH measured 122 dBA at 10 feet (3 m) and 98-105 dBA at 100 feet (30 m)¹⁰². That is where the commonly quoted "about 120 dB at 10 feet" comes from.

The crew hears it too. With roof-mounted speakers, NIOSH measured 109 dBA at the driver and 91 dBA at the patient. Moving the speakers to the grille cut that to 87 dBA at the driver and 76 dBA at the patient¹⁰². NIOSH recommended grille or bumper speakers, closed windows, and using the siren only when necessary¹⁰². A 2007 study found passenger compartment levels could still exceed 90 dBA⁹⁵. For reference, the same NIOSH report cites the OSHA permissible exposure limit of 90 dBA as an 8-hour time-weighted average¹⁰² - a workplace limit, not a figure to compare directly with a single siren pass.

Speaker count matters: dual-speaker electronic systems average about 3 dB more than single-speaker systems⁹⁵.

Who sets the siren standards?

In the US, SAE J1849, "Emergency Vehicle Sirens," is the recommended practice for laboratory test procedures, requirements and guidelines for single-speaker electronic and electromechanical sirens on authorized emergency vehicles. SAE issued it in July 1989, stabilized it in October 2012 and revised it in February 2020¹⁰³. The federal ambulance specification, KKK-A-1822, is issued by the General Services Administration - the agency that requested the 1985 NIOSH study¹⁰².

The 2007 edition, KKK-A-1822F, requires a combination electronic siren and public address system "capable of producing a continuous warning sound at a minimum level of 123 dB, A-weighted, at 10'," with dual speakers mounted outside the vehicle in the bumper or hood area¹⁰⁴. That is a floor, not a ceiling, and the bumper placement matches what NIOSH recommended in 1985¹⁰².

Elsewhere, standards follow local choices. Singapore's Ministry of Home Affairs told parliament on January 12, 2026 that its emergency vehicle sirens "meet the SAE J1849 international standard"¹⁰⁵. Germany uses DIN 14610⁹⁹.

Why can't I tell which direction a siren is coming from?

What you hear: a siren that seems to come from everywhere at once, then appears from the street you weren't watching.

Your brain locates sound with three cues: the difference in arrival time between your two ears, the difference in level between them, and the way your outer ear filters sound depending on its direction (the head-related transfer function). All three work best on broadband sound, which spreads energy over many frequencies⁹⁵.

A classic siren is close to the opposite: a fairly pure tone sweeping through a narrow band. Sirens also use relatively low frequencies on purpose, because low sound bends around corners and through openings better⁹⁵. That helps a siren reach you, but not tell you where it is. In a city, the sound also bounces off building faces (see what hard walls and tall buildings do), so the timing and level cues arrive scrambled. Treat that last point as a reasoned explanation rather than a measured result.

The broadband idea has made it into backup alarms: OSHA told a manufacturer in 2004 that a "white noise" backup alarm can comply with construction rules as long as it warns workers in time¹⁰⁶. The full story is in construction, backup beepers and leaf blowers.

What are outdoor warning sirens, and why do they test them?

What you hear: a long, steady tone from a pole-mounted siren, usually at the same time on a set day; or, in a Japanese town, a gentle melody at dusk.

Fixed outdoor sirens warn of disasters or attack. The traditional civil defense code used a steady tone for an alert and a wavering wail for attack; many towns also tested fire sirens daily at noon, and many communities switched fire sirens off after pagers arrived in the 1970s⁹⁵.

Hawaii sounds its statewide outdoor warning sirens on a schedule. The test on Friday, May 1, 2026 sounded at 11:45 a.m. as a one-minute steady "Attention Alert Signal," paired with a test of the Emergency Alert System live audio broadcast¹⁰⁷.

The Hawaii Emergency Management Agency runs the siren test monthly, together with an Emergency Alert System test, "normally on the first working day of the month," at 11:45 a.m., with a one-minute steady tone, per a 2017 agency advisory¹⁰⁸. Its July 2024 release followed the same pattern - Monday, July 1, at 11:45 a.m., a one-minute steady "Attention Alert Signal" - and asked the public to report siren problems to county civil defense agencies¹⁰⁹.

Japan does it with music. The tune you hear at the end of the day in most Japanese towns is a test of bosai musen ("disaster wireless"), the municipal loudspeaker network, nicknamed goji no chaimu, the 5 p.m. bell. More than 90% of municipalities have one. The test plays at 5 p.m. in winter and moves to 5:30 or 6 p.m. as days lengthen, using one of 32 standard tunes, with "Yuyake Koyake" a favorite. The national system was launched after the 1964 Niigata earthquake and is linked to J-Alert, introduced in 2007¹¹⁰.

The chime doubles as a signal for children to head home¹¹⁰. "Yuyake Koyake" began as a 1919 poem by Uko Nakamura and was set to music about five years later; some Tokyo wards have their own chimes, and one, Bunkyo-ku, has none, according to Metropolis¹¹¹. Japan's other designed melodies, at stations and crossings, are in sounds made on purpose.

Do car alarms actually stop theft?

What you hear: a cycling pattern of whoops, honks and chirps from a parked car, usually with nobody coming to check.

The evidence collected by critics says mostly no. A March 2003 report by the advocacy group Transportation Alternatives, "Alarmingly Useless," cited authorities' estimates that 95% to 99% of car alarms are false. It also cited a 1997 Highway Loss Data Institute analysis of 73 million vehicles that found alarm-equipped cars "show no overall reduction in theft losses"¹¹². The same report said noise made up 83% of 97,000 calls to the New York Police Department's Quality of Life Hotline in 2001, with car alarms near the top, and estimated the cost of car alarm noise in New York City at $400-500 million a year¹¹². Those cost figures are an advocacy estimate.

The politics were not one-sided. In 2003, New York City Councilwoman Eva Moskowitz introduced a bill to outlaw car alarms, with fines of up to $2,100 for frequent offenders; the city's Department of Environmental Protection and the NYPD testified against a ban¹¹³.

The bill that became law came from Councilmember John Liu. Int. 81-A made it illegal to sell an audible car alarm that does not shut itself off within three minutes or that can be set off without anyone touching the car, and barred anyone other than a manufacturer from installing one. Mayor Michael Bloomberg vetoed it on August 16, 2004, and the Council overrode the veto on September 28, 2004, enacting it as Local Law 43 of 2004. As enacted, fines run from $500-1,000 for a first violation to $2,500-5,000 for a third or later, enforced by the NYPD and the Department of Consumer Affairs¹¹⁴.

In Boston

Boston's city code limits car alarms: an alarm that is plainly audible 200 feet away must shut itself off automatically within five minutes, with a $50 fine, according to a 2016 printout of the noise chapter (16-26)⁶². The same chapter exempts noise from emergency vehicles during an actual emergency⁶². The city routes car alarm complaints to the Boston Police¹¹⁵.

Elsewhere in the world

• Germany: one legal emergency tone, the DIN 14610 two-tone horn; yelp allowed since 2024 only as a police and customs stop signal⁹⁸.
• Singapore: emergency vehicle sirens meet SAE J1849, per the Ministry of Home Affairs (January 2026)¹⁰⁵.
• Japan: daily melodic tests of the bosai musen disaster speakers, in more than 90% of municipalities¹¹⁰.
• United States: multiple electronic tones, SAE J1849 testing, and in some police fleets the low-frequency Rumbler¹¹⁶⁹⁶.

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