Thanks I ordered one today from a Subaru Dealership. Only 18 of that sensor in the country. Got it far, far cheaper than what Halfords was quoting. Cheers

There are quite a good selection on this eBay search https://www.ebay.co.uk/sch/i.html?_nkw=22629AA070&_sacat=0&_from=R40&_trksid=m570.l1313 I'm sure the same sensor will have been used on numerous other vehicle makes and models

Thanks Mr B. Ill try to replace the unit. after that I will bypass… If you have any reliable resources on bypassing this unit Id be grateful to receive. i much appreciate you taking the time to respond to thread

As mentioned before you can buy a used alarm main unit and plug it in and program your fobs to it and set a new pin code for it if so wished. Only plus with that is remote locking be functional again . Downside is you still dealing with 20 year old european electronics and as it basically can leave you stranded it best pulled out and binned as saves same issue twice (siren board corroded/faulty by leaking P9 battery being super common). I done repairs both ways for customers (option tended to be driven by their preference on alarm and locking). you can add a remote locking system if pull alarm but that adds cost . A working M30 used module is cheapest fix with everything same as owners already use to . You can find used M30 modules pulled from Subarus for around 80 to 150 quid, it must come with pin or a working keypad ( I like a keypad with it as then you got a third keypad that can be used for parts in your key should one of yours fail and it generally easier programming using an existing remote than using pin code) . You got options and none are technically difficult or needs specialist equipment thus the cost to resolve it either way is not crazy money . If you half competent and can google info you could swap alarm module or even bypass it to get running as it really nothing more than cutting and joining some wires ...

Mr B, many thanks for response. An auto electrician (via email) has advised removing unit and a helpful call from Subaru Replacement Key Services seems to confirm alarm unit ECU is dead ?? >> >>No LED in dash, no light flashes on keypad when inputting digits before key inserted. When key inserted the keypad light flashes several times on each digit entry. Alarm DEFINITELY working. its loud and annoys neighbours and puts me off trying to do anything. If I can get a replacement unit is it an easy swap out ? I dont possess a multimeter but inexpensive. Im not overly technical, or experienced. If replacement failed, Id go to a bypass route and sacrifice remote central locking. Currently only the drivers door is locked by key… As immobiliser system appears completely unresponsive but alarm sounds what would you recommend next? Thanks