Battery went flat causing alarm to sound and won’t stop after changing battery

My 318i alarm decided to start going off and would not turn off with key. I recharged battery and when hookup terminals horn goes off. How do I reset
My car has an automatic transmission.
Experienced mechanics share their insights in answering this question :
The most common methods to deal with this situation are to put the key in each door and lock and unlock to reset the alarm. You may need to do this in the trunk or hatch lid as well. The second method is to disconnect the battery, put the key in the ignition, turn it to run and reconnect the battery. Once the battery is connected, start the car. If either of these do not work, you will need to contact someone to diagnose the alarm system. Diagnosis of alarm systems takes an experienced technician. It involves a scanner, knowledge of automotive electronics systems as well as experience with your particular make and model.

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You typically will not need to do anything to reset your car alarm after a battery change, but it should automatically reset for you. Some vehicles or alarm systems may require you to push a reset button on the alarm box that may be located near the steering wheel.
Disconnect the battery

Your car alarm runs off power from your car`s main battery or a backup battery. Disconnecting the battery can stop your alarm, but we again only recommend this step if nothing else works AND if you understand how to safely remove a car battery.

It`s normal while you`re doing it. If it keeps happening after you think you`re done: That would suggest that your battery clamps are loose (either on the posts, or the wires), or that you didn`t clean them properly, or that you need new clamps.
Regardless of the type of system that you have, there are several ways to determine when it is time to change the battery. Although there is some variation in battery longevity, most batteries in alarm systems today will last somewhere between three and five years.
Use Your Key and Both Lock And Unlock The Driver`s Side Door

Locking and unlocking the driver`s side door can reset the switch and cause the alarm to cease. If the driver`s side door doesn`t work, try the passenger door. Further, try turning your vehicle on as well.

If your ECU controls the anti-theft system, disconnecting the battery may lock you out of your car. Like desktop computers and most other electronics, disconnecting the battery cable for a short period will not fully reset your ECU due to the residual power remaining in the circuits.
If your car horn starts going off on its own, it`s probably because the battery needs to be replaced.
The brain and alarm features may be wired to the car`s main battery, but they usually have a backup power source as well. This hidden battery kicks in when somebody cuts off the main power source (by clipping the battery cables, for example).
The battery may need to be replaced. An alarm will chirp every 30 to 60 seconds for a minimum of seven days. With a “low battery” announcement, disconnect the unit and replace the batteries.
Charge your empty battery for 24 hours. It is best practice to test your alarm system while it is still in test mode.
There are some cars that will recognize the key from you simply turning it back and forth in the door`s cylinder. It is best to try both methods: holding the key in the door, as well as turning the key both ways to disable the anti-theft system.
Most car alarms are designed to reset when the key is turned in the ignition or when the start button is pushed. Lock or unlock your car: If you hit the lock or unlock button on your remote, your car alarm should automatically turn off. Hit the panic button: This one sounds a little counterintuitive.
Most systems will begin beeping or chirping as a result of a total power outage or failure to recharge the system backup battery. For many of our most popular systems, beeping alarms and low battery trouble beeps can be silenced by pressing the [OFF] or [#] buttons from the keypad.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Battery went flat causing alarm to sound and won’t stop after changing battery
ANSWER : The most common methods to deal with this situation are to put the key in each door and lock and unlock to reset the alarm. You may need to do this in the trunk or hatch lid as well. The second method is to disconnect the battery, put the key in the ignition, turn it to run and reconnect the battery. Once the battery is connected, start the car. If either of these do not work, you will need to contact someone to diagnose the alarm system. Diagnosis of alarm systems takes an experienced technician. It involves a scanner, knowledge of automotive electronics systems as well as experience with your particular make and model.

Battery died, does it have anything to do with alarm going off and not stopping when it was recharged? 2003 GMC Yukon
ANSWER : Hi there – yes, a security/alarm system that continues to beep/honk/whatever, is draining your battery, just like a light that is left on. Most cars make the alarm system go off when the battery is replaced – or when the battery is run completely flat, then jumped off. To shut off the alarm when you jump it off or replace the battery, the following generally works: shut off the engine, close all doors, lock the vehicle from the driver door with the key, not the remote. Wait 1 minute. Open the driver door with the key (not the remote function), then start the engine with the key. For most vehicles, this will shut off the alarm system. The "battery" light flickering on and off could be a loose serpentine/accessory belt, a failing alternator, or a failing voltage regulator. Most auto parts stores will check the battery and alternator, although the alternator must be removed to test. The easy test is to see if the alternator is pushing system voltage to about 14.5 volts with the engine at a fast idle. If this is the case, then check for a loose belt, or something that is draining the battery when the car is shut off. This problem can be diagnosed by connecting an ammeter to the positive (red) battery cable, observe the current drain (likely less than 1 amp), then, one at a time, remove each fuse, check to see if the current drain has dropped to near 0, then reinsert the fuse. This process should identify the faulty circuit in most cases. The specific components on that circuit can then be checked for current drain problems. A professional mechanic, like YourMechanic, can come to your location, and perform this procedure for you, and replace/repair the failing component.

My alarm keeps going off and car won’t start after changing battery, what can be wrong?
ANSWER : Hello, and thank you for writing in. When dealing with alarm and starting issues, you are really dealing with a miscommunication with the alarm system. If you have a spare key, try using it to disarm the system and start it. You may also want to try key cycling ("Off"-"On" without starting), as it will make the computer reset its communication with all of the modules. It usually takes 3-5 cycles to achieve any kind of reset. Often with newer models, giving the vehicle some time to sit and trying again later helps the computer work through its programming, and it can reset itself. The longer the vehicle sits, more of the systems will shut off, and more of these systems have to restart when you try again (as some systems do NOT turn off when you turn off the engine, and they continue to use electricity to hold memory). One of the other ideas to consider is that the new battery is not fully charged, or your battery terminals are not allowing for a proper connection (either because they are loose or dirty, or have a bad ground connection). If none of the above gives you control over the vehicle, then you need to seek professional help. Contact our service department for a quote or to schedule an appointment.

Car alarm is going off when using clicker to unlock the car
ANSWER : The content theft deterrent (CTD) alarm will sound when either the door is opened without using the key to unlock the driver’s door, or when the door is unlocked without using the unlock command from the keyless entry transmitter. My guess is that, for some reason, the control module is not recognizing your key fob. Instead of locking your doors with the remote, try locking them manually. This should solve your problem. You can also deactivate the CTD by doing the following:

Press either door lock switch.
Use the key to unlock the driver’s front door.
Press the unlock button of the transmitter.
Insert the key into the ignition and turn the vehicle on.

Of course, these are work arounds. For a permanent fix, I suggest you have a trained professional diagnose your initial starting issue and other causes to repair your vehicle.

I have Chrysler 300c. Battery light came on, changed battery and alternator but power still getting drained and battery light still comes on.
ANSWER : Hi, thanks for writing in. This may be a sign of a failing starter relay. The starter relay is a small unit near the starter that directs power to the starter from the battery. When this fails, it may cause a clicking sound and will not allow the starter to engage the flywheel when you turn the key. I would suggest having a professional from YourMechanic come to your home to diagnose your starting issue to determine the solution to get you back on the road.

I have changed battery. I think I put non compatible battery initially and it’s start car alarm loud not turned off with remote ac
ANSWER : As long as the nominal voltage of the battery is 12 volts, it’s compatible. Of course, you need sufficient energy storage capacity, too, which in your case is probably around 850 cold cranking amps. As long as you did not reverse the positive and negative terminals (reverse polarity) when you installed the first battery, the battery is not incompatible. When new batteries are installed, inasmuch as any computer settings are lost, there can appear to be electrical problems, but such are not a fault of the battery. If, for example, you are having problems with the engine immobilizer system (security system) you may see a security warning light on the dash. If the warning light is on, to temporarily override the immobilizer system, see these instructions.

If you are experiencing electrical problems with other components, please simply request an electrical system diagnostic and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

Crank no start
ANSWER : Hey there, thanks for writing in about your 2003 Ford Explorer. It sounds to me like you either have no fuel or bad fuel at the injectors, or no spark to spark plugs. Try to narrow the problem to one of these possibilities. If you just got fuel before it dies, then you may have excessive water in the fuel. Take a fuel sample and let it settle in a cool place to see if water is in fuel. You already ruled out many components, but you have to double check and make sure that each test was done correctly. If you’d like further help with this, my recommendation would be to have a certified mechanic, such as one from YourMechanic, thoroughly diagnose the no start issue in person in order to have this properly resolved.

Battery dead truck wont start after alarm being messed with.
ANSWER : With all the playing around, the battery going dead more than once, and it being over 5 years old, I would try replacing the battery first.

After the battery is replaced, lock all the doors and then unlock the vehicle with a remote or door keypad if you have one equipped. Next, using an original key, see if it will start. If it doesn’t then the vehicle may have locked you out. In this case, only a WDS scan tester at a dealer can regain access to the passive anti-theft system for you. Unfortunately this would mean that you’ll need to tow it to a dealer.

If you decide to get this fixed or would like a second opinion on this, get the car looked at by a qualified technician, such as one from YourMechanic. A mechanic can perform these checks to properly diagnose your dead battery and fix it accordingly.