What are these for?

AlexD333 · 12-05-2014, 19:52

Been meaning to ask for a while, (might get banned for too many posts)

Any ideas? Doesn't seem to emit a sound

geoffdown · 12-05-2014, 19:56

Quote:

Originally Posted by AlexD333

Been meaning to ask for a while, (might get banned for too many posts)

Any ideas? Doesn't seem to emit a sound

Interior alarm.

Lazy-Ferret · 12-05-2014, 20:24

Thats the ultra sonic alarm parts, that get disabled if you press the alarm switch on the dashboard.

Sweety · 12-05-2014, 20:26

As Clive has said it's the alarms ultra sonic's

Blocky10 · 12-05-2014, 20:35

Yep. They look better with the cover taken off and posted to me! :-D

Sent from my C1905 using Tapatalk

AlexD333 · 14-05-2014, 22:54

Thanks for the replies guys, I missed this post all together somehow

So what, it emits a siren inside if someone is breaking in?

kitchenman · 14-05-2014, 22:59

I think it senses a change in air pressure or motion and set off the alarm
I had on in my Citroen, passing lorries when I was parked set it off, the slipstream reduced the pressure inside the car, alarm thought the door was opened, even passing cars set it off if a window was slightly open on the road side PITA

solarman216 · 14-05-2014, 22:59

no one is a transmitter the other is a receiver all the time they communicate without interference every thing is good but broken window or other disturbance = alarm, Rick

AlexD333 · 14-05-2014, 23:03

Quote:

Originally Posted by solarman216

no one is a transmitter the other is a receiver all the time they communicate without interference every thing is good but broken window or other disturbance = alarm, Rick

Ah there we go, thanks. And thanks kitchen

Lazy-Ferret · 14-05-2014, 23:21

They are very clever, I built one when I worked at Kent & Canterbury University, They work on the Doppler Effect, which is what you hear when a car passes. As it comes towards you, it sounds like someone has turned the Treble up, and you hear a higher frequency, then as it passes, the treble gets turned down, and the base turned up, and you hear a lower frequency, but in reality, the car made the same noise all the way along.

Basically, one side is a transmitter, which fills the car with ultra sonic sound waves, and the other side listens out for the reflected waves coming back at the same frequency. If something in the car moves, the reflected waves will either increase or decrease in frequency, depending on which way the item is moving in relation to the transmitter. If this increase or decrease falls within specific parameters, it sets the alarm off.

The great thing is, air movement should not normally set it off, but if the air movement blows something hanging in the car, such as an air freshener hanging from the rear view mirror, or a passing lorry shakes the car and makes something move, then it will be set of erroneously. If a window is open, then the sound will not be reflected back until it hits something outside the car.

14-05-2014, 22:59	#8
solarman216 Off road maniac Join Date: Dec 2009 Location: Bexhill on Sea Vehicle: Y60 Patrol Me, 3 ltr Mrs Posts: 17,432	no one is a transmitter the other is a receiver all the time they communicate without interference every thing is good but broken window or other disturbance = alarm, Rick __________________ Ex banger racer now off road maniac Lokka on the front with manual hubs Diff lock on rear 3 inch SS straight through exhaust Manly winch bumper with 13000 lb winch 10 spike ground anchor, with multiple straps and blocks Super strong body cills capped with scaffold pole 20% stronger springs all round aggressive off road tyres on wheels so just swap. Aim to get stuck and be completely self sufficient in extraction, love getting muddy, 2ft deep is good but rare.

12-05-2014, 20:24	#3
Lazy-Ferret Senior Member Join Date: Jun 2012 Location: Sevenoaks, Kent Vehicle: Terrano 2.7TDi SE Touring Posts: 5,221	Thats the ultra sonic alarm parts, that get disabled if you press the alarm switch on the dashboard.

12-05-2014, 20:26	#4
Sweety Senior Member Join Date: May 2013 Location: Northumberland Vehicle: Terrano 2.7TDI SE LWB Posts: 3,604	As Clive has said it's the alarms ultra sonic's

12-05-2014, 20:35	#5
Blocky10 Senior Member Join Date: Mar 2014 Location: Welcome to Norwich, a fine city Vehicle: 2004 Terrano 3.0 SVE Auto Posts: 3,601	Yep. They look better with the cover taken off and posted to me! :-D Sent from my C1905 using Tapatalk

14-05-2014, 22:54	#6
AlexD333 Senior Member Join Date: Jan 2014 Location: Uk Vehicle: 2004 Terrano 2.7 TDI Posts: 7,847	Thanks for the replies guys, I missed this post all together somehow So what, it emits a siren inside if someone is breaking in?

14-05-2014, 22:59	#7
kitchenman Senior Member Join Date: Jan 2011 Location: Essex Wescliff Vehicle: maverick 1994 2.7 TD Posts: 1,278	I think it senses a change in air pressure or motion and set off the alarm I had on in my Citroen, passing lorries when I was parked set it off, the slipstream reduced the pressure inside the car, alarm thought the door was opened, even passing cars set it off if a window was slightly open on the road side PITA

14-05-2014, 23:21	#10
Lazy-Ferret Senior Member Join Date: Jun 2012 Location: Sevenoaks, Kent Vehicle: Terrano 2.7TDi SE Touring Posts: 5,221	They are very clever, I built one when I worked at Kent & Canterbury University, They work on the Doppler Effect, which is what you hear when a car passes. As it comes towards you, it sounds like someone has turned the Treble up, and you hear a higher frequency, then as it passes, the treble gets turned down, and the base turned up, and you hear a lower frequency, but in reality, the car made the same noise all the way along. Basically, one side is a transmitter, which fills the car with ultra sonic sound waves, and the other side listens out for the reflected waves coming back at the same frequency. If something in the car moves, the reflected waves will either increase or decrease in frequency, depending on which way the item is moving in relation to the transmitter. If this increase or decrease falls within specific parameters, it sets the alarm off. The great thing is, air movement should not normally set it off, but if the air movement blows something hanging in the car, such as an air freshener hanging from the rear view mirror, or a passing lorry shakes the car and makes something move, then it will be set of erroneously. If a window is open, then the sound will not be reflected back until it hits something outside the car.