How do you reset your alarm on bmw 5 series after battery disconected?

To reset the alarm on a BMW 5 Series after disconnecting the battery, first, reconnect the battery and then insert the key fob into the ignition. Turn the key to the "On" position without starting the engine, and wait for a few moments. This should reset the alarm system. If the alarm still triggers, you may need to use the key fob to lock and unlock the doors to re-establish the system.