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Alarm Keeps Going Off - But No Indicators Flashing & No Immobiliser

Stevearcade

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Just a heads up for people, as this may be useful in case is happens to anyone else!

This morning on my drive to work, I'd been on the road about 30 minutes and stopped for coffee at a garage. When I returned to my car I pressed the button on my key fob, the car unlocked as normal, but the alarm sounded.

The indicators weren't flashing and the immobiliser wasn't active. I was able to start the car drive away. The alarm continued to sound for about 30 seconds then stopped for about ten seconds and then carried on sounding for another 30 seconds and then stopped for ten seconds again. This repeated for about 10 minutes. Then it stopped and stayed stopped.

I was sitting in a traffic jam the whole time and it was somewhat stressful. I called my Honda garage and spoke with mechanic there, alarm going in the background all the while. He said the alarm system has its own battery system, which like the normal car battery charges as it drives. If/when it runs flat, it charges up next time the car starts. Until the unit has a satisfactory level of charge, the alarm will continually go off in it's usual sound cycle. I don't know if this is an intended design or a glitch in the design. Either way it's seriously annoying! It stopped going off while I was on the phone to him. I will see if the alarm does this again when I leave work. I hope it won't!

However, this throws up a few questions:

1) I'd been driving for half an hour. Why did my alarm's battery run flat?
2) Did it instantly discharge itself while parked up at the garage? If so, there's a problem!
3) Is my alarm's battery at fault, if so this will keep happening until I get it replaced - apparently not too expensive???
4) Is the whole alarm unit at fault? Apparently they're very expensive to replace!

I'm obviously hoping it's a one off. Perhaps it was caused by moisture ingress? We have had unusually heavy, wet weather this last couple of weeks.

Obviously, if there's more to report I'll keep the thread updated, but just in case anyone else has the same issue, don't instantly panic, it's likely to be the alarm's battery recharging. It could point to another underlying problem, but in the instance it happens, just keep the engine running and drive around a bit to charge the alarm battery, just like you would a normal car battery.
 

freddofrog

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It will be the battery in the alarm ("bell-box"). As rechargeable batteries age, they eventually just "dive" for no reason .....and sometimes come back to life again ....briefly. This applies to car batteries too.

I had a 10-year-old caravan and the alarm did the same thing in that.

My house is 13 years old, the battery in the bell-box died a few years ago, as soon as the mains power goes off, the bell-box starts to sound (even though the alarm is not set).

It's a common "feature" on alarms, I think it's basically to let someone know that the battery is old and needs replacing. I'm waiting for the same thing to happen on my Accord.
 

Stevearcade

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So do you reckon I should just order a new battery for bell box?
 

chew

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I've had this happen before. I don't know whether it was a coincidence but it happened when the batteries in my key fob died. I changed them and disconnected the car battery for a while and it was fine. This was about a year ago
 

Stevearcade

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Called HoldCroft on a price. The battery isn't sold a separate unit from the rest of the alarm so the whole unit would need to be replaced at a cost of over £700 (with TA discount) so realistically, if the problem gets worse, open up the unit and disconnect the siren in the alarm. The other functionality will remain, such as locking and immobiliser, which really is key. As this morning's drive to work shows, no one cares when a car is driving down the road with its alarm blaring! Haha!
 

freddofrog

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chew said:
The issue in that thread is caused by the main car battery being slightly below voltage when you open the door (with the alarm set). It is possible that the problem that Steve had is the same i.e. the main car battery in his car is on its way out, but since he had been driving for 30 minutes before he locked the car, unlikely.

But it is also possible that battery in the sounder unit is on its way out.


Stevearcade said:
Called HoldCroft on a price. The battery isn't sold a separate unit from the rest of the alarm so the whole unit would need to be replaced at a cost of over £700 (with TA discount) so realistically, if the problem gets worse, open up the unit and disconnect the siren in the alarm. The other functionality will remain, such as locking and immobiliser, which really is key. As this morning's drive to work shows, no one cares when a car is driving down the road with its alarm blaring! Haha!
The sounder unit in the Tourer is in the rear offside wing. It is separate from the alarm control itself (most alarms work this way).

The sounder unit has its own battery. If it receives a signal from the alarm control unit to go off, then it will go off. Also, if it has been told that the car is locked, then it will also go off if it loses communication with the alarm control unit (this is the situation where the main car battery voltage has dipped, as above).

But if the battery in the sounder unit is old, then I think that the sounder will go off when its own voltage drops (this is because someone might cut the wires connecting it to the main car battery, and short them).

If you are sure that the main car battery is 100%, then the best thing to do is to get to the sounder unit (with the alarm unset), and disconnect the sounder unit. If you can, you might want to remove the sounder unit and open it up.
 

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Cheers Brian. Yeah, I was thinking along those lines. As it's not possible to buy a separate battery for the unit and it wouldn't be worth getting one from a scrap yard as it would probably be duff or old and on its way out anyway, if the problem persists, I'll pull the internal panels apart, get to the unit and disconnect the siren. Realistically the noise feature of the car's security feature doesn't really account for a whole lot, as was proved by the fact I was driving a car with the alarm going off for about ten minutes and no one batted an eyelid.

If someone really wants to break in to a car, the alarm won't discourage them. If someone really wants to and knows how to steal a car with an alarm and immobiliser, they will! My car's a 13 year old Honda that's starting to look a little tired and has a child seat and McDonald's Happy Meal toys on the back seats...

I don't worry about it too much ;)

As for the issue in hand, it hasn't reoccured with my drive home. I've also made two short quick journeys this evening and the car was fine. My car's battery is 3 and half years old and the car is driven nearly every day. I'm pretty confident it's still ok.
 

freddofrog

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Yeah I agree, the siren is only there to indicate that someone has broken a window or forced a lock to get into the car. The immobilizer is the main security element, which stops the car from being nicked without the key.

I've found this on the Honda workshop DVD ....




In there it says to remove the right "trunk" trim panel (to get to the siren). Depending on how difficult it is to remove the trim panel, I wonder if it would also be possible to get to it by removing the rear wheel and the plastic wheel arch.

Anyway, it is a 4-pin plug. The way that the siren would go off (when armed) is when
A. one or more of those wires is cut/disturbed before the siren has received a dis-arm instruction on pin 2.
B. an intruder alert is received from the MICU on pin 2
C. a signal is received from the ultrasonic sensor on pin 3 without having received a dis-arm on pin 2.

My understanding of the low car battery volts scenario is ***ociated with condition C.

For some reason, you may have experienced condition C e.g. maybe you left something on in the car that dipped the car battery volts a bit (enough to prevent the MICU from sending a dis-arm).

But IMO it is possible that the battery in the siren can itself be faulty, such that it does not receive the dis-arm properly.

They should have made it possible to lock and unlock the car using the key in the driver's door, without arming the siren.
 

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Hi guys,
This same thing happened to me last night (and has happened before).
The alarm kept going off (siren) but the indicators did not flash.
I couldn't do anything to stop it, but it finally stopped, until this morning.
Randomly pressing the lock and unlock buttons stopped it.

I have a new car battery fitted last year Nov/Dec.
However I did notice the last time this happened, disconnecting the car battery did quieten the siren - I guess my alarm battery is dying as well.

Any idea where this is located on a 2007 saloon?
Hoping to removing the battery or replace it with some NICAD or other rechargeable battery.

Many thanks.
 

freddofrog

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^ siren is in same place on the saloon as on the Tourer in #9, same way to access it.
You'll have to take the siren out and open it up to get to the batteries.
 

muppet9966

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Many thanks freddofrog.
I will be popping out shortly to try to remove the panels to access the siren - lets hope that's easy and I don't break anything.
Short term to disconnect the 4pin plug.
Then longer term to remove the siren and replace the battery within the siren.

Fingers crossed!
 

freddofrog

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yep just pull the plug off and it should stay quiet, but of course, not if you do it with the system armed LOL
 

muppet9966

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Well found the siren, and pulled the plug.
The siren sounded until I opened it and disconnected the battery.
On closer inspection, the battery does seem to have drained, its 7.2V 250mAh.
The voltage drops to 4.9V when loaded with 150Ohms (approx. 50mA draw).

I will be ordering some small cell batteries to replace the battery.
I'll keep you all posted.

I'll post some pictures up shortly to ***ist anyone.
 

freddofrog

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^ that was quick, and yeah it does seem as if the siren batteries in a lot of 7th gens will be on their way out

Pics will be really useful.
 

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Oooh, what batteries does it take exactly? Could you provide a link please?
 

muppet9966

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Just taken some photos of where exactly it's located, with photos of the battery.
As soon as I get to a pc I'll upload these.

Unfortunately it doesn't look like you can buy the battery as its probably custom made.
But 3x 2.4v cells should do the job and fit nicely. Just need to check the current rating.

Pritesh K
 

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Pritesh, you're a legend mate. Nice work.
 

chew

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Was the pictures ever uploaded for this? I have the same problem tonight.
 

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I don't think so. Pritesh, did you ever get round to uploading these pictures?
 

muppet9966

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Sorry guys, I have uploaded photos and have even ordered the battery.
I haven't got around to fit the battery in yet, but will do shortly.
I couldn't remember my login password either which didn't help.

I'll post these later today, but as freddofrog has mentioned someone has beaten it to me.

Pritesh
 

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Thanks very much. I think I'm gona try charging my battery and resettibg first. My battery is on charge now. Hope it works. If not I'll be doing this.
 

freddofrog

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chew said:
Thanks very much. I think I'm gona try charging my battery and resettibg first. My battery is on charge now. Hope it works. If not I'll be doing this.
Based on personal experience very recently, if you had to disconnect the main car battery to charge it up, once you reconnect the main car battery, the siren will go off. Whatever you try to do, the siren will keep going off. Best thing is to shut all the doors and bonnet, and leave it and it will stop after a few attempts. But when it has stopped, even though you will be able to lock and unlock the car with the button on the fob, as soon as you open the door to get in, it may go off again. If it does that, then shut the door, and the siren will stop again after a few attempts. Then wait for between 10 to 30 minutes for the main car battery to charge up the battery in the siren.
 

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Apologies for this late post.
On the saloon Accord, the alarm siren is located in the boot, drivers side behind all the carpet/trim.
It is held on my 2 screws/bolts (circled):



Once the alarm siren is removed, you can disconnect the wiring.
As soon as you do this, if there is charge in the siren battery the siren will sound.
Mine sounded very low. I decided to connect the wiring back - I should have had some ear defenders, as it was ear piercingly loud.
This was because the main car battery is powering the siren, not just the backup internal battery in the siren.









The side metal brackets can be removed to uncover 2 screws.
Removing these screws will allow you to take apart the siren.





The battery is seen in green.
I crudely drew approx. 50mA through a 150 Ohm resistor and the voltage dropped too low, approx 4.9V

These look like they are 6 cells, equating 7.2V, 250mAh.



The battery looks custom made for Honda, and you cant get this.
However you can make up the same capacity batteries using 3 cells.
I found these from CPC, 2.4V 250mAh.


Three of these will give 7.2V 250mAh.



I have ordered mine, but haven't had the time to solder these together and create a single larger cell.
My siren is still currently disconnected, but I will hopefully fit all this back together.

I hope this helps some of you.

Pritesh.
 

Stevearcade

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Pritesh! You legend! This is probably going to become a very appreciated thread as I expect in the coming years as our 7th gens get older, more and more of these incidents will occur. Great work man.
 

chew

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Great guide pritesh . Charging my battery and resetting the alarm worked for me this time but eventually I'm going to replace these batteries or remove it all together.Just concerned about insurance if I did do that.
 

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I now have a problem with my alarm! If the car is locked or unlocked, when. I open any door, the alarm sounds. If I sit in the car and wait for the alarm to stop (with the car still unlocked) and wave my arm - triggering the ultra sonic sensors - the alarm goes off again. Any ideas anyone?
 

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My car does this if I leave the car standing for a couple of weeks with the main battery disconnected, which causes the battery in the siren to go flat. If I reconnect the main battery and open the car door the siren goes off, but it stops after a few goes. If I sit still in the car until it stops and then move about, it goes off again. The only way for me to deal with it is to start the engine, shut the doors, and leave it for about 20 mins while the siren battery recharges.

The problem that you describe sounds similar. As well as the siren's battery being the cause, it might be the ultrasonic sensor itself that has gone faulty. But if you look at the circuit diagram below you'll see that the siren and the ultrasonic sensor both get +12V from the same feed, and since the sensor doesn't have a battery in it, the battery in the siren might be low enough to cause it to mis-read the line from the ultrasonic sensor.




IMO it's best to get to the siren and take it out and check the internal battery pack, as in #25.
 

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Thanks for the reply Brian. What you say seems to add up. I left the car standing for a week last week, and when I came to start the car, the battery was totally dead - which indicates a dodgy battery. When I went home last night the siren went off. I set off for home expecting the siren to sound again, but it didn't, and today it's behaving itself, so maybe it's charged itself. Still a bit confused as to why the ultra sonics set the alarm off though. I'll wait and see what happens.
 
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