Burglar Alarm with EXTREMELY LOUD siren

[Ecklar]

I am building a burglar alarm system. Yes simple enough, but I want it to be so loud that it's weird, sick and really scary.  The thought is to have the room (building) internal siren to be so loud that it shocks and scares trespassers and makes it difficult for a person to think and continue with any action except a desire to flee.  I'm thinking of limiting the system to 12 volts so I can run it off of a power supply backed up with 12 volt rechargeable batteries so it will work if main power is cut or generally down; i.e., after a natural disaster like a storm.

It seems most available sirens come in around 110 - 120db.  Why not 135db?  And it would be nice to have a noise source that could project the noise sound pressure such that you'd still get obnoxiously loud sound 100 feet from the source.  I want the noise source to be no larger than about 1 cubic foot. The smaller the better so it is as inconspicuous as possible.  I'd love to use an old air raid siren, but they seem huge and probably require more than 12 volts.

With that in mind do you have any ideas as to what sound source I could use in my alarm system to create a situation that would be difficult and truly shocking for intruders? 

Thank You

[rs20]

The sheer malice in this question is pretty disgusting. In any case, by my rushed calculations 135 dB SPL @ 1m corresponds to over 40 watts of pure audio power from an isotropic emitter; after the inefficiency of the speaker. I can't really think of anything complimentary to say about this statistic.

[Ecklar]

Volcano, something along the lines of Krakatoa.

It is pretty hard to break the laws of physics. 

If you could create magic super loud speakers that are directional (or not), long/short distance,  tiny, run off 12V / small batteries,  and cheap, don't you think that speakers for things like rock concerts wouldn't be the size of refrigerators, et. al., and your air raid siren wouldn't be huge and take lots of power?

Volcano and magic speakers.  Yeah.  That's brilliant.  I'm asking for the best idea within the limitations or even pushing the criteria a bit if viable.  Also, I never suggested that I wanted to fill a auditorium with 10,000 screaming fans.  I AM looking for the most obnoxiously loud effective solution ideas to my project.  Please, I am looking for ideas I may have overlooked....  not beer talk.

Thanks

[Ecklar]

The sheer malice in this question is pretty disgusting. In any case, by my rushed calculations 135 dB SPL @ 1m corresponds to over 40 watts of pure audio power from an isotropic emitter; after the inefficiency of the speaker. I can't really think of anything complimentary to say about this statistic.

If by malice you mean an effective way to physically arrest or repel an intruder to save life and property, then yes, that is what i AM seeking.  However, I would really appreciate and am looking for a concrete product, device or build solution.  I am not trolling for pedantic analysis that goes nowhere.

Thank You

[Ian.M]

Compressed gas cylinder with a rupture disk, a carefully designed whistle that works with up to 2000psi input pressure and a solonoid to strike the pin to pierce the rupture disk.  With a big enough cylinder to get enough gas flow and a larger whistle and a horn to direct the sound, it would be possible to reach lethal dB levels.

Alternatively an array of electrically detonated thunderflashes scattered around the area triggered by a psuedorandom sequencer - think weaponized Vetinari clock! 

[Ecklar]

I can assure you you will need to shock the burglars into a sonically induced stupor because your neighbours will make certain they see nothing. The first response to someone selfish and stupid enough to put such a loud noise source into an urban environment is to refuse to help them justify it.

Get better locks, CCTV or a monitored alarm system.

Better locks stop only children.  CCTV deters absolutely nobody.  Monitored alarm systems average response time from authority averages 27 minutes.  Any ideas on actual physical device solutions greatly appreciated. Please.  I am looking for engineering ideas and not tricked out social commentary or beer talk.

Thank You Wilfred for your contribution.

[Ecklar]

Compressed gas cylinder with a rupture disk, a carefully designed whistle that works with up to 2000psi input pressure and a solonoid to strike the pin to pierce the rupture disk.  With a big enough cylinder to get enough gas flow and a larger whistle and a horn to direct the sound, it would be possible to reach lethal dB levels.

Alternatively an array of electrically detonated thunderflashes scattered around the area triggered by a psuedorandom sequencer - think weaponized Vetinari clock! 

I DID consider the air horn but I want to stay as close to 1 cubic foot device dimensions as possible.  The horns, compressor and tank to make this work will come out to easily over 5 or 6 cubic feet and I don't believe will run off my 12 V battery backup.  If there are some small air horn system I've overlooked, maybe that could be the solution, usually YOU need the compressed air tank and requires more volumetric space than I have. 

[MK14]

Compressed gas cylinder with a rupture disk, a carefully designed whistle that works with up to 2000psi input pressure and a solonoid to strike the pin to pierce the rupture disk.  With a big enough cylinder to get enough gas flow and a larger whistle and a horn to direct the sound, it would be possible to reach lethal dB levels.

Alternatively an array of electrically detonated thunderflashes scattered around the area triggered by a psuedorandom sequencer - think weaponized Vetinari clock! 

I DID consider the air horn but I want to stay as close to 1 cubic foot device dimensions as possible.  The horns, compressor and tank to make this work will come out to easily over 5 or 6 cubic feet and I don't believe will run off my 12 V battery backup.  If there are some small air horn system I've overlooked, maybe that could be the solution, usually YOU need the compressed air tank and requires more volumetric space than I have.

My reply (which I just removed), was a JOKE. I did not think you would be crazy enough to consider it.

Surely it is against the law where you live ?

[NiHaoMike]

There are automotive air horns that will easily fit in a cubic foot for the whole kit. Other than that, maybe firecrackers?

I would also suggest a bunch of Xenon strobes set to flash at 5-10Hz. Such a flash rate is very disorienting.

[MK14]

[Ecklar]

There are automotive air horns that will easily fit in a cubic foot for the whole kit. Other than that, maybe firecrackers?

I would also suggest a bunch of Xenon strobes set to flash at 5-10Hz. Such a flash rate is very disorienting.

I like the Xeon idea to enhance the effect.  Any ideas on which air horns would fit the small space?  Somehow either a compressor and compressed air tank would be needed so I am thinking that would push me beyond the 1 cubic foot.  Frankly, that is my starting point. A little beyond the 1 cubic would be OK.

[Ian.M]

There's also https://en.wikipedia.org/wiki/Blaster_(flamethrower)

Legal in some jurisdictions . . . . .

[Ecklar]

Compressed gas cylinder with a rupture disk, a carefully designed whistle that works with up to 2000psi input pressure and a solonoid to strike the pin to pierce the rupture disk.  With a big enough cylinder to get enough gas flow and a larger whistle and a horn to direct the sound, it would be possible to reach lethal dB levels.

Alternatively an array of electrically detonated thunderflashes scattered around the area triggered by a psuedorandom sequencer - think weaponized Vetinari clock! 

I DID consider the air horn but I want to stay as close to 1 cubic foot device dimensions as possible.  The horns, compressor and tank to make this work will come out to easily over 5 or 6 cubic feet and I don't believe will run off my 12 V battery backup.  If there are some small air horn system I've overlooked, maybe that could be the solution, usually YOU need the compressed air tank and requires more volumetric space than I have.

My reply (which I just removed), was a JOKE. I did not think you would be crazy enough to consider it.

Surely it is against the law where you live ?

Crazy?  When brainstorming, all ideas are worth consideration on an engineering basis.  Air horns are illegal for passenger cars, but not necessarily for certain alarm situations if zoning allows and that depends on the local.  If the proper alarm could save life and/or property in a non-lethal fashion, I don't think there is anything crazy about that.   If you have serious property and people that exist in a dangerous situation and maybe it's your familly, it's perfectly sane to put your best effort into the effort mate. 

I really didn't know you were joking.  I just thought you had no idea for the actual size of the air horn system since I've already evaluated and dismissed it as not feasible.

[IanB]

Loud sounds will only work once. The second time the intruders will come back with ear defenders. If you are in the USA suitable hearing protection is easily purchased from any shooting range or gun shop.

[MK14]

Crazy?  When brainstorming, all ideas are worth consideration on an engineering basis.  Air horns are illegal for passenger cars, but not necessarily for certain alarm situations if zoning allows and that depends on the local.  If the proper alarm could save life and/or property in a non-lethal fashion, I don't think there is anything crazy about that.   If you have serious property and people that exist in a dangerous situation and maybe it's your familly, it's perfectly sane to put your best effort into the effort mate. 

I really didn't know you were joking.  I just thought you had no idea for the actual size of the air horn system since I've already evaluated and dismissed it as not feasible.

When I said "Crazy", I meant it in two different senses.

Firstly that to hurt the burglars was a bad idea and could lead to you being prosecuted.
But enough about that aspect of crazy for now.

The other crazy sense, was that the idea was not very practical (massive tanked air horns and stuff). Such as you mentioning being too big, etc.

I've experienced VERY loud conventional sirens (electric piezo/speaker), indoors. They definitely made me want to leave the area. So I think it can be done, with conventional sirens, if placed indoors, and they are the loud variety.

They can be relatively cheap (perhaps $10 to $20 or so), small (about 6 inches square, and a few inches deep). Also fairly easy to connect to your alarm system.
This is what I think (but maybe a bit louder), was in the last youtube video I linked to above.

tl;dr
At least for me, it makes me want to leave the area, quickly and not stay there.

[jonovid]

It seems most available sirens come in around 110 - 120db.  Why not 135db?  And it would be nice to have a noise source that could project the noise sound pressure such that you'd still get obnoxiously loud sound 100 feet from the source.  I want the noise source to be no larger than about 1 cubic foot.

  Why not 135db? ,  the Law, your sky high cast of haveing public liability insurance for the permanent hearing damage. or killing someone in a mantrap!  you go to jail.  So a bank of piezoelectric elements running square wave at 2kHz  to 3kHz will cause hearing pain. disorientation, sound perception confusion.    a Note that young people's hearing is the full 20 Hz to 20 kHz. & that most breaking and entering is by people under 25 yo. -must be fit  so a sweeping  3kHz to 20 kHz at 110db will do. 

[ruairi]

The owner/user of your proposed alarm system will set it off accidentally and suffer permanent hearing damage.  This is a dreadful idea.

[BradC]

Back when I was an apprentice we had a job installing and commissioning a security system for a lovely but eccentric gentleman worth a *lot* of money. He had some innovations like staged wire rope gates on his driveway that would trap intruding vehicles, sequenced floodlights that made the property light up like a disco to alert the neighbours to an alarm and a few other interesting features.

In his boathouse/garage he had a very large horn he wanted hooked up. It was rated well in excess of 135dB and consumed an inordinate amount of power. We provided a power source, contactor, terminals and interconnecting cable but politely refused to hook it up or test/commission it. The theory was to cause immediate damage to any intruder. I believe he hooked it up, but we wanted no further part in the endeavour. I don't know where he got it and I never asked.

I did some work recently for an LNG plant with an LRAD (Long Range Audio Device) that was rated to provide a painful level of sound at 5Km using a focused beam. Again, not interested in the how or why, just decided I didn't want to play in that sandpit.

[ez24]

Try what the police use, a stun grenade.  It works on the principle of sound, so loud it stuns, thus the name.  I am sure an electronic activated one can be designed and built.  I like the idea.  Maybe you would get a fine for using it.      They were used at my house to wake people up ha ha ha  (they work)

[helius]

Ordinary smoke or CO detectors are unbearably loud when tested up close. These devices are less than 200 cm³ and run off 4.5V. They could possibly be extended with appropriate horns to cover a larger area at longer range and still be effective.
The issue highlighted by IanB applies: once attackers know that the system is in use, they will use ear protection. I suggest you use multiple modes of action to make the response unpredictable.
An electronic noise system can easily emit warning chirps before it goes full blast. Attackers won't know what the warning means, so they won't cover their ears before the alarm activates, but property owners will.

[DaJMasta]

Please don't make it, even if you find a suitable noise maker.



The vast majority of alarm soundings will be false alarms or routine tests, and unless you're trying to protect something with no hearing and no people within half a mile or more, there will be hell to pay every time it sounds (provided you can fit such a device into a cubic foot that can fire more than a few times without damaging itself).  110 dB, your basic low end estimate, is enough to cause physical pain in some people and measurable hearing loss with just a couple minutes exposure.  120dB is enough to cause pain in most, instant temporary hearing damage, and long term hearing damage with only 30 seconds or so of exposure - think a nearby thunderclap, working in an active steel mill, or small arms firing close to you.  The range you're talking about is akin to the deck of an active aircraft carrier, a gun going off within just a couple feet of your ear, fireworks going off next to you, or an air raid siren in the same room as you.  135dB and thereabouts is enough to instantly do permanent hearing damage, cause significant physical pain, and is nearing the physical breaking point of the ear drum.

The alarm WILL misfire, they always do.  Sound this loud WILL damage the hearing of anyone within a few dozen yards and piss off anyone for several hundred more.  This is enough sound pressure to start picking frequencies and nearby materials carefully because it can damage them, and even if there are no explicit laws against it on the books for your area, you are likely to be sued by any potential invader, if not your neighbors.


So yes, it's probably possible to meet your goals, but if you really think it's beneficial to risk so much damage and pain on accidental victims and unprepared criminals..... just hire a security detail, clearly you need something better than an automated system and they will be much more acceptable in your community and much less likely to injure someone you're trying to protect (if the idea really is for protecting a residential property).  Please do not implement this.

[ez24]

.... a gun going off within just a couple feet of your ear

How about use 12ga shotgun shells, take out the buck shot and stuff in a small rag.  Then use a small heating coil to fire them off.  A few of these going off will cause pee stains on the floor.  And probably easier to make than a flash bang grenade. Have a loud high pitch siren that ramps up (I would try 2 sec) and at the peak, have a shell go off.   I think this would be pretty nasty.

A ramping screaming alarm with explosive sounds - sounds cool.  umm Kickstarter time

Here is an idea to get started



If you are wimpy here is another idea ( 8.6 million views ! )



Man can you just imagine this going off with shot gun shells - oh yeah !

[MK14]

.... a gun going off within just a couple feet of your ear

How about use 12ga shotgun shells, take out the buck shot and stuff in a small rag.  Then use a small heating coil to fire them off.  A few of these going off will cause pee stains on the floor.  And probably easier to make than a flash bang grenade. Have a loud high pitch siren that ramps up (I would try 2 sec) and at the peak, have a shell go off.   I think this would be pretty nasty.

A ramping screaming alarm with explosive sounds - sounds cool.  umm Kickstarter time

There already was a kickstarter project, very similar to how you just described. There was a thread about it here.

You have to be careful, otherwise you can be prosecuted for laying down man traps (terminology may vary by country).

EDIT:
Here it is:
https://www.eevblog.com/forum/crowd-funded-projects/bike-mine-a-literal-mine-on-your-bike/

[Ian.M]

Party poppers repacked with finely ground dried Ghost Chillis + a job lot of solenoids to fire them.  No hazard to the neighbours, but your burger wont be very happy.  Add the 110dB warbling sirens and strobe lights for maximum effectiveness.     Personally, if you do experiment with this the first priority would be to develop an effective RFID lockout system for the more vigorous parts of the system so although the alarm can be activated, the nasty bits cant easily be triggered if there is a family member in the room wearing a tag.

[MK14]

the first priority would be to develop an effective RFID lockout system for the more vigorous parts of the system so although the alarm can be activated, the nasty bits cant easily be triggered if there is a family member in the room wearing a tag.

[Family Member]
I've forgotten my necklace (with built in RFID tag). Better go back inside and get it.
Oops I've set the alarm off.
Then walks towards the man traps, "nasty bits", WITHOUT the RFID tag.
Boom BOOM boom.
Broom BROOM brooms to tidy the mess.
boo BOO boo, family member says about new alarm system...

tl;dr
I'm not entirely convinced that this is a good/safe/legal idea.