View Full Version : Am I setting off those car alarms?

08-29-2000, 03:12 PM
No, this isn't like extinguishing streetlights (https://academicpursuits.us/classics/a4_047.html) with bodily emanations.

I recently purchased a 1999 Mustang GT. It has an unusually loud 4.6L V-8 engine. I admit, I really enjoy the sound and the feeling - but that's not my point.

The building I work in has a six-level underground parking garage. As I rumble past in first gear, I sometimes notice car alarms going off. Is the sound of my engine setting off these alarms?

Has anybody else encountered this, or is it a case of my "only noticing the van when it's on the corner?"

I figure the acoustics involved are unusual, but certainly not unique. At Texas A&M, whenever we fired the cannon during a football game, car alarms for miles around would go off. I imagine the phenomena are related.

Long time RGMWer and ardent AOLer

08-29-2000, 03:30 PM
This is quite possible. I've noticed that Harleys and buses can have same effect.

08-29-2000, 03:31 PM
Oops, forgot to put the "the" back in!

08-29-2000, 04:07 PM
It is a result of people being paranoid enough to set the sensitivity on their alarms too high. I used to sell and install alarm systems and made sure that I explained the idea of false alarms like that causing people to ignore car alarms.

Like you, I park in a garage every day and the exhaust on my V-6 Sonoma sets off alarms occasionally. Granted, it isn't stock, but it is a little quieter than your 'stang. I used to delight in driving around the mall setting off car alarms by cranking my stereo, too.. I am glad I grew out of that, but it was fun while it lasted. :)

08-29-2000, 04:48 PM
You certainly could be. A buddy of mine often sets off nearby car alarms with his truck--in open parking lots.

He finds it entertaining, as he hates car alarms.

08-29-2000, 06:34 PM
Yeah, that happened to me too. The guard came running. I need to tell him I didn't do anything.

08-30-2000, 12:14 PM
Is it illegal to set off the alarms? You know, touching them so the alarms go off? Hmmmm. Can you play any songs if you touch the right cars in the right sequence?

08-30-2000, 03:21 PM
Why does sound set them off?

Several years ago when there were fewer car alarms, there was a pickup with one in a parking garage one night where I parked to go to dinner. If you got close to it, the horn honked, lights flashed, & a voice said "step back from the car". You only had to get within 6 feet or so (such as in the next parking space) to make it go off. Many people hadn't seen that kind of alarm before, so people were walking up to it to make it go off, so they could see what it did. After dinner, I walked by the truck again & nothing happened, so I guess the alarm ran enough to drain the battery.

08-30-2000, 04:26 PM
Tampa: The car had a motion detector. It quit going off after awhile because most alarms will disable a trigger if it goes off too many times within a certain amount of time. I had one on my last car that chirped if it detected motion with a foot of the car, and went off if it detected any motion within the car.

Sound sets it off because the low frequencies from an exhaust or bass will vibrate the shock sensor, making it think the car is being moved, causing it to go off.

09-08-2000, 04:58 PM
We watched the Fourth of July fireworks this year from the parking lot at Sea World in San Diego (tried to beat the traffic out at the end; didn't work). Every time they'd fire a rocket with a concussion charge along with the sparkly stuff, there would be an answering cacophony of alarm sounds from all over the lot, answered in turns by the raucous laughter from my kids.

So, sure, why couldn't a loud exhaust in a closed garage set off alarms? If you can feel the vibrations in your chest, a sensitive motion detector can do so, too.

09-08-2000, 05:13 PM
Modian - Vibrations can also set off a glass sensor. My VW had this feature. To test whether or not a car has glass sensors, smack the windshield lightly with your open palm. The alarm usually won't go off, but you'll hear a warning buzz.

09-08-2000, 06:36 PM
My car used to do that. It was an old Dodge V-8 (360, 4V) with dual exhausts and glasspacks. :D

Just starting my car would set off alarms. If I actually revved it.... *sigh* I miss that car.

09-10-2000, 12:01 PM
Trembler-switch alarms are particularly sensitive when the car is parked on a non-level surface. If your parking ramp is like most, it doesn't have leveled floors, its slightly angled, like a, well, ramp. This means the trembler switch is already half-cocked, and takes less force to activate. Any vibration could set it off.
BTW, you reactivated memories of my old '65 Mustang GT convertible that I had in high-school. Everyone said they could always hear me coming from a mile away, that dual exhaust had a very distinct sound. The new models are engineered to emulate that sound, but it just isn't the same.

09-10-2000, 12:52 PM
Is it illegal to set off the alarms? You know, touching them so the alarms go off? Hmmmm. Can you play any songs if you touch the right cars in the right sequence?

Some "performance artist" somewhere beat you to it. I believe he eventually earned himself a misdemeanor bust for "disturbing the peace" or something like that.

Timothy Campbell
09-10-2000, 02:41 PM
One thought occurs to me: standing wave.

Your car probably rumbles at some sub-sonic frequency, and this sets up a standing wave between the roof of the parking garage and the floor. Sounds echo very well in parking garages, so I don't think this idea is completely off-the-wall. (No, it's off the ceiling! There, beat you to it.)

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