Steve,- Many thanks for the excellent explanation of the system, armed with the additional knowledge I tried today to re-create the original event but without success, everything works OK, it locks, it unlocks, the alarm works, the motion detector works, if I unlock with the mechanical key the alarm starts to wind up but as soon as I put the key in the ignition the alarm stands down which is all as it should be. Batteries in the key were replaced in February , even so at the time of the event I did blame them until the problem turned into the 'cant stop the alarm nightmare'! The odds of having more than one fault must be very high so I guess that whatever happened (the lock function and the alarm glitch) must be linked in some way even if the systems are seperate. Hopefully it wont re-occur, certainly it is impossible to diagnose when the fault is no longer there.
The only remaining symptom is the red led in the motion sensor/towaway switch which is now permanently lit, nothing in the owners information discribes any situation where this led is lit continuously so I guess something is wrong. I did try disconnecting the vehicle battery for 10 minutes in the hope of creating a re-set but no such luck. If this remains the only problem I can live without being able to switch off the motion sensor or towaway function .
Again thank you for your excellent system explanation,
XP190, yes it is quite interesting, as I understand it the key is a sort of 'passive transponder or resonator' for the EIS security signal, a bit like the anti theft store tags used on expensive items to stop people shoplifting but more elaborate, I Guess Steve could give you a more technical explanation.