All electrical systems require voltage to operate, normally 11.5-12v, computers wont function properly below that.
take the battery back out
This happened to me just recently. Not sure why. To resolve I disconnected the battery for 15 minutes reconnected and problem resolved.
your battery is dying or is dead
If you set the alarm (i.e. lock the car) and then disconnect the battery, the alarm will go off. If you disconnect the battery when the alarm is not set (i.e. when the car is unlocked) the alarm will not go off. (So don't try to nick a locked one).
To reset the alarm system on your BMW after a battery died, first replace the battery with a new one. Then, use your key fob to unlock the car, which should help reset the alarm. If the alarm continues to trigger, you may need to start the engine and let it run for a few minutes. If issues persist, consult your owner's manual or a professional for further assistance.
To jump-start a 2006 BMW 325i, first ensure both vehicles are turned off. Connect the positive (red) jumper cable to the positive terminal of the dead battery, then attach the other end to the positive terminal of the working battery. Next, connect the negative (black) cable to the working battery's negative terminal and attach the other end to a metal ground on the dead car, such as an unpainted bolt or bracket. Start the working vehicle, let it run for a few minutes, then attempt to start the BMW.
To jump start your BMW X5, first ensure both vehicles are turned off. Connect the red positive cable to the positive terminal of the dead battery and then to the positive terminal of the working battery. Next, connect the black negative cable to the negative terminal of the working battery and attach the other end to an unpainted metal surface on the dead vehicle to ground it. Start the working vehicle, let it run for a few minutes, and then attempt to start your X5.
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By using your key to unlock the door.
because you need a new battery for your car
Some alarms systems have a protection function which will prevent starting the engine is somebody tried disconnect the battery and connect it again. Also what might happen is that your alarm system doesn't have memory in the case if you disconnect the battery. Thus, if you do disconnect the battery it will reset the alarm system to the default factory settings. By default, the alarm system will block starting the engine.
the alarm in my 528i BMW turns on and off. what can cues this. thank you...