central locking alarm fob

Yes they can be reprogrammed.

I believe it says in the manual that after changing the battery (and if you fumbled more than 30s doing it) you need to re-teach the key to the locks.

I don't have the manual handy, although it might have been in one of the maintenance manuals I have been reading lately...will try to find out.

The factory-fit alarm/remote-locking fob is the one integrated with the key. Early versions were infra-red and later versions used radio frequency.

I don't think that any of these has an LED light in the fob and I think they have a built-in safety cut-off in case you hold the button pressed accidentally for too long, to prevent draining the internal battery.

For these fobs, the procedure to re-synchronise them to the car is described in the car owner's manual and consists of set of procedures with the ignition key in different positions etc

You must be referring to an after-market alarm unit. In which case, you may need to consult the manufacturer of the alarm. From your description of the fob it could be a dealer-fitted alarm, probably intended for BMW models not having a factory alarm option. Or, it could be a 3rd party alarm provided with matching BMW emblem on the fob. Probably your best bet would be to see if a dealer parts-dept might recognise the model of alarm or try doing a search in google to see if you can find other references to this type of alarm. In some cases additional UK-sourced alarm units are fitted where the factory unit has not been certified to Thatcham categories, if this is important for a particular insurer.

Finally, it's only alarms with rolling-codes which require resynchronization of the fob to the the alarm unit. Many early RF units had static codes.

Also, there is a small possibility that, coincidentally, your fob is damaged (?)

I've done some searching for you and apparently it seems to be one of 4 different alarm models commonly fitted to the E36, by UK dealers. Each has a different reset procedure:

".....in the UK BMW used 4 different alarms.
is the remote part of the key? if it is you need a complete key
is it long and thin with one button? a dealer or Sigma alarm place can recode
is it a rectangle with a corner cut off and one button?
is it a rectangle with a corner cut off and two buttons?
...."

http://www.pelicanparts.com/bm…ects-92-Alarm-Install.htm

Anyway, see the end of the the thread in this link. It seems to be the same as yours:

http://www.usedcarmart.co.uk/forum/showthread.php?p=55542

There's also some reset instructions buried in the first link, but they may or may not work with your model of alarm (US units may have been different). Anyway, it can't hurt to try them:

Close all the doors, the trunk, and front hood.

2. The alarm must be placed into disarm mode (not armed and not activated). If this reprogramming procedure doesn’t work after attempting it a few times, you may have to pull out the glove box and disconnect the harness to the alarm unit (or pull the fuse) to reset it and put it into disarm mode.

3. Remove the key from the ignition.

Start code-learning mode

4. Open the rear trunk, and leave it raised and open.

5. Open the driver’s door and sit down in the driver’s seat.

6. While sitting in the driver’s seat, close the driver’s door.

7. Turn the ignition switch on, then off, five times. Do not start the engine. Simply turn the switch to the on position each time so all the dash warning lamps illuminate. Important: All five cycles of the ignition switch must be performed within 10 seconds.

The entire sequence of steps (one through seven) must be performed within 45 seconds. When the steps are performed properly, the red alarm LED will illuminate continuously, and the alarm siren will sound a single chirp. This indicates that the code-learning mode has been started. Do not start the engine at this time.

Register remote ID codes

8. While remaining in the driver’s seat, open the driver’s door.

9. Close the driver’s door.

10. Press and release any button on the remote control unit you wish to register with the alarm unit. The alarm LED indicator will turn off momentarily to indicate that the ID code has been registered with the system.

11. For additional remotes (up to a total of four), repeat steps 8 through 10.

Exit the code-learning mode

12. Open the driver’s door, and get out of the car, but leave the door open.

13. Close the rear trunk.

14. Close the driver’s door. The alarm status LED will turn off, and the siren will sound a chirp twice.

15. The registration process should be complete and you should be able to use all the remotes that you registered with the system.