Car alarm keeps triggering - any help, please?

Alan_Cross

My wife has bought an old 04 plate Hyundai Accent as a temporary runabout and it seems to do all that's asked of it ... BUT... the car alarm keeps sounding off which is making us unpopular with the neighbours... AND it's come to us minus the owner's manual.

The car is supposed to lock by key fob remote and give one flash of the indicators. Unlocking gives two flashes. Simple, eh?... Only problem is that locking by this method usually produces flashing lights and blaring horn after five to ten minutes... which is hardly making us popular with the neighbours.

Sometimes, I notice, the car will lock without showing a flash from the indicators... and then we have peace and quiet.


I'm at my wits end and just can't work out what's going on. I've heard it said that it might be something to do with the alarm 'arming' itself but what the hell does that mean?

Any help greatly appreciated.

AdrianC

"Arming" means the alarm is switched on. If you lock the car with the key in the door, the alarm probably won't be armed - just the car locked.

There may be a button inside the car to disable the ultrasonic sensors, which monitor the interior airspace of the car, basically by bouncing a sound wave around and "listening" to the echoes. Those can be easily triggered by something as simple as a spider moving around in front of one of the sensors.

Marktheshark

Flat back up battery in the sounder unit ?
You have to locate it and unplug it, usually behind the plastic panel under the wheel arch.

uknick

I have every sympathy with you for this sort of problem.

My car did this once or twice in May of both 2012 and 2013, and only in May. It never did it before, or since. Garage could find no fault with it on the diagnostics. But, as it didn't do it last May I assume whatever ghost/gremlin was in the car has left for new pastures.

I'd download the owner's manual from the internet to see how the alarm should be set. If you're doing it correctly, which I'm sure you are, then try the following; (if you've done all this I apologise for teaching you how to suck eggs);

- make sure windows are completely shut; wind can cause the interior sensors to trigger the alarm
- turn off the interior sensors to see if it's a fault with them
- check the car battery; a worn battery can cause voltage drop which as far as the alarm is concerned could be someone trying to break into the car
- make sure all doors, bonnet and hatchback are securely shut


If all that is OK, then I suggest getting it to the dealer to plug in the diagnostic and see if a fault comes up.

Or, if you have a home recovery service, call them out to plug in their diagnostics machine. This should be covered in the price, it was in mine, as it is fault with the car which could mean you could have to leave it without the alarm switched on.

Marktheshark

As said they have what is known as a "sounder unit" in this box of tricks is a back up battery that is supposed to keep the alarm sounding if someone inplugs the car battery to try and shut it up.
However when the battery in the sounder unit goes flat, the alarm mistakes the battery in the sounder going flat as someone opening the door.
Locate the unit by googling and unplug the damned thing.
Job done, if it bothers you new reconditioned ones are on e-bay

colino

As above, especially if it is an add on and not "factory fit" (UK dockside commissioning bay) with clever voltage drop units a sounder battery is seen as a voltage drop and it will go off until it is switched off or it goes hoarse. Do check all of the switches individually though first if the sounder is particularly difficult to get to (they should be), check if it has a stand-alone under bonnet switch and eliminate the cabins ultrasonics by shutting off the heater flaps too.
Ideally disconnect the sounder, nobody pays the slightest bit of attention to car alarms now, unless it is disturbing their beauty sleep.

facade

Try pressing the lock button once, then after about 1/2 a second press it a second time. This usually disables the internal sensors, and you get a long flash of the indicators.

Otherwise, agree with the sounder idea, it happened on my Vectra years ago, it was because the internal rechargeable battery died, unplugging the sounder did the trick.

Strider590

Yeah, i'd be looking at the sounder unit first too, they have small recharging Ni-MH battery packs, which gradually decreases in capacity and usually give up after around 5 years.

When they start to fail, the alarm thinks it's being tampered with and goes mental, especially in cold weather.

It can also be the early warning sign that the car battery itself is on the way out, the alarm sees the car battery voltage drop and again it goes mental.

In the summer months, it's often caused by insects inside the car, walking/flying in front of the sensors.

In spring/autumn it's often water interfering with the boot/door/bonnet switches.

You might be able to stop this by locking the doors manually, or by pushing the lock button down and then closing the door.