Sound of da police
June 21, 2013 1:22 PM   Subscribe

Why do police cars use different variations of their sirens? Sometimes it's a full on siren, but other times it's "woop...woop...woop" with a second or two in between. And other times they don't turn on the sirens at all but just haul ass down the street with the lights flashing. I thought it was about reducing noise to the neighbors if it's late at night, but that isn't the case. I haven't been able to figure out a pattern. Is it something about the urgency of where they're going to?
posted by RabbleRabble to Grab Bag (15 answers total) 4 users marked this as a favorite
I think it is about what clears intersections the fastest.
posted by timsteil at 1:23 PM on June 21, 2013

Yeah, sometimes it'll be silent, with just the lights, until it hits a busy intersection and it needs people to get out of the way. Then all of a sudden the siren will go on, startling everybody...
posted by Melismata at 1:26 PM on June 21, 2013

Best answer: Also used if multiple cops are travelling to a crime scene from different directions. The different sounds lets cops know when other cops are approaching. If all the cops were using the same sounds their siren could very well drown out the siren of other cops, bad news for intersections, converging traffic etc.
posted by Max Power at 1:27 PM on June 21, 2013 [4 favorites]

Around here les gendarmes have the constant annoying siren for racing down the street and the extra annoying "get the fuck out of the way because I am coming through this here intersection red light be damned" siren.
posted by Sternmeyer at 1:27 PM on June 21, 2013 [1 favorite]

It's also just playing around. There was one driver in ithaca thirteen years ago who would create hiccups with his siren. Like every time. I lived halfway up the hill, so I heard them all.
posted by Namlit at 1:28 PM on June 21, 2013 [2 favorites]

Mod note: Folks, please keep responses focused on answering and not just speculating/relating anecdotes. Thanks.
posted by restless_nomad (staff) at 1:34 PM on June 21, 2013

Best answer: Note: all of this is based off of 10 year old emergency vehicle operation course as an EMT in PA.

The siren is not supposed to be used when there's no need to clear traffic. Just lights are sufficient. There is a tendency for the siren to cause the driver to go faster. The siren is required at intersections for safety reasons.

As for the multiple tones, they are present so a person, upon hearing a siren in the distance but not seeing an emergency vehicle doesn't get lulled into complacency that the emergency vehicle is going elsewhere. The change in tone makes a person recheck for the emergency vehicle.
posted by bfranklin at 1:39 PM on June 21, 2013 [6 favorites]

(and, obviously, I'm assuming the police have similar operating procedures to an ambulance)
posted by bfranklin at 1:40 PM on June 21, 2013

When I worked for the NYPD lab they had us take driver training in case we ever had to drive a city car so they gave us a crash course on the the lights/siren even though we really weren't supposed to use them per-say.

The cars were set up so you could turn on just lights, or lights and siren, and the horn was hooked up to that short sort of trill siren so you could activate a warning sound quickly/as needed, which you were supposed to do whenever you were pulling out into traffic.

I am sure it's different in different areas but the rules we learned were similar to what bfranklin was talking about above...
posted by Captain_Science at 1:50 PM on June 21, 2013

Best answer: To quote Wikipedia:
Most modern vehicles are now fitted with electronic sirens, which can produce a range of different noises. Police driving training often includes the use of different noises depending on traffic conditions and manoeuvre being performed. In North America for instance, on a clear road, approaching a junction, the "wail" setting may be used, which gives a long up and down variation, with an unbroken tone, whereas, in heavy slow traffic, a "yelp" setting may be preferred, which is a sped up version of the "wail". Some vehicles may also be fitted with airhorn audible warnings. Also in some European countries, where a hi-lo two tone siren is the only permitted siren for emergency vehicles, a "stadt" siren will be used in cities where it has loud echo that can be heard from blocks away to warn the traffic an emergency vehicle is coming, or a "land" siren will be used on highways to project its noise to the front to produce more penetration into the vehicles ahead to alert the drivers.
And from Yahoo Answers UK:
Why do the sirens on police cars change? Does each emergency service have it's own siren?

In the UK now legislation says vehicles have to have the (new) directional sirens. Such sounds of the new sirens in the UK are the Wail, Yelp and Piercer. The wail is the long and slow tone used to draw attention from distance, yelp for junctions and the Piercer is the fastest tone and most alertive.

All emergency vehicles will soon have the same sirens as the old ones are being replaced.
posted by Celsius1414 at 1:57 PM on June 21, 2013 [2 favorites]

Unusual tones also catch the attention of drivers much more effectively. Old-style sirens are such a well-known sound that many people don't register hearing them. Newer style sirens are designed to catch the brain's attention.
posted by quince at 4:19 PM on June 21, 2013

There was an article in the NYT which also mentions the "Rumbler" -- a siren which is meant to almost be felt. That can be especially helpful in big cities where the wail of sirens can almost become background noise when they are so common. It also explains a bit about other sirens as well.
posted by This_Will_Be_Good at 5:16 PM on June 21, 2013

I know our local police do NOT use sirens unless necessary for safety. They used to have a much more liberal siren policy (assuming there even was one) but now they just, as you say, haul ass with the lights on when responding to urgent calls. It's probably largely about catching perps unaware, although not waking up everyone on the way to the call is nice too.

There are also increasing issues with car stereos being loud enough that occupants do not hear safety sirens (not to mention other distractions). Thus, the Rumbler [CNN]. (On preview: Jinx!)

Here's a pretty good primer on police sirens and the way that they're used nowadays (and a related article about police driving, by a retired cop).
posted by dhartung at 5:19 PM on June 21, 2013

There are times when they will leave the siren off to be more discreet when they're responding to something like a reported burglary in progress.
posted by ambient2 at 2:05 AM on June 22, 2013

Trained as an ambulance driver in another life...
Siren sound variance also done so all drivers involved do not get fooled into thinking that a siren is echoing, when in fact the echo is a separate other response vehicle or vehicles. The variance allows a break in the sound rhythm of the sirens for drivers to become aware of response vehicles approaching from other directions.
posted by No Shmoobles at 8:51 PM on June 22, 2013

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