Bmw alarm keeps going off

Quite often people forget to attach the ground cable that goes under a bell housing bolt , check there first.

Hi it seems like key is not responding. Its been immobilised.
you need to get some one down to get the key to be read by the car. Possibly need the car key reprogram

Check you have not left any wires off or trapped any when putting gearbox back in

Reason I'm even bringing im up is because Ive seen it. Could u possible have a dead battery in your remote?

http://www.pelicanparts.com/BMW/techarticles/BMW-3-Series-E46/02-BASICS-Replacing_Your_Drive_Belt/images_large/pic01.jpg
Here you go

For Remote locking problems I would start troubleshooting the cheap things first.
Replace the battery in your key(s).

there is a button on the left hand side of your turn signal lever that says bc. there is also a button on that switch that can be pushed up and down. start your car finger up on the small switch on your turn signal until you see the tire light symbol. once you see the symbol in you instrument cluster press the bc button once then hold it until it says resetting. drive the car and the light will go off in a matter of minutes maximum.

ive just discovered this same problem with my bmw 320d this morning! any theories why it wouldnt lock? would be very helpful

Hi , you can lock your car without activating the allarm by using the key to lock your car manually ( not the remote ) , the most common alarm fault on this car is the hood switch, if you change this buy one for a bmw Z4 model which is slightly longer and garrentees a contact when the hood is closed, hope this helps regards mark

locking and unlocking with the key is to deactivate the alarm not activate it, the alarm is activated every time the car is locked with the remote automatically, u need do nothing else