Immobiliser key kit swap help

[Tonybandit]

Hi. Im new to this site but having problems with my alarm.
I've just had a new key coded and it didn't solve my problem.
My problem is.... key fob would not open the doors.
I've had water get in to the car and gone under the passenger
Seat and now this problem.
I've spoken to a few people about this and I'm looking to gain as much information as I can before I go ahead with replacing anything. Info so far says I must swap the engine ecu the alarm ECU and the key fob from the same car. I've found an engine ecu with the same part number but finding an alarm ecu with the same part number is proving hard. As long as I fit the matching engine ecu with fob then the alarm part number is irrelevant as long as the alarm ECU is the match to the engine ecu that I fit.
I hope this is clear to someone haha. Am I right in thinking this??? Has anyone done this swap?

Many thanks.
Tony