Anti theft system beeps constantly on a 03 z4

Have you tried fuse for dashboard

follow this link as is a common reset procedure
How to Turn off Theft System on Cars

The security, antitheft or lock picture/icon is a visual indication that something in the car's antitheft system is failing. In most GM cars and trucks there is a hidden system that most people are unaware even exists. From the moment you put your key in the ignition, there begins a constant line of communication between your key's security chip or transponder, to the ignition's lock cylinder, and then to the car's TDM (Theft Deterrent Module). These 3 parts are in CONSTANT communication. If the key is in the ignition, then these parts are sending signals to each other. The security light illuminates when that signal gets broken, even just for a second. When the signal breaks, the car misinterprets this as an attempt at theft and goes into antitheft mode. The car thinks its being stolen or hotwired because it is not getting that signal from YOUR specific key. This is why the security light turns on and shuts down your vehicle. This link explains it pretty well.
http://www.diy-gm-security.com/

contact the manufacturer of the after market anti-theft system for advice. without knowing the make and model information, no one can help you further.

Hi
Unfortunatley once you have entered a code wrong 3 times in a security coded radio, it is rendered U/S, this is an anti theft device so if someone steels your radio, and tries to enter code incorrectly it has a special chip that burns out ( or what ever it realy does) and then they cannot sell it or use it.

Sorry....

if anti theft module not communication with scanner or diagnostic hook up then your vehicle will probably not start till thats corrected and clicking sounds like relay from security system opening up and shutting down power for starting system

I need to change headlight bulb in a 2004 BMW Z4 coupe. Does anyone know where I can find out how?

Not trying to steal your solution, but trying to clean up the unanswered page:
There are two possible answers here:
The simple one:  Use your remote control's "unlock" button to reset the anti-theft system.
or a more comlex one that seems to work: (From the original post)"I found out that you remove the horn fuse, shut the doors, put the key in and unlock it two times then put the fuse back in...it resets the anti theft..."