944 Alarm issues?

[1964SW]

I have a 944 1989 2.7Ltr (non turbo) and appear to have a intermittent problem with the Alarm ECU? Can the alarm ECU become intermittent? or does it work or not?

When I start the car sometimes ..it sets the alarm off and the engine will not start. If I get out of the car lock it then unlock it this appears to clear what ever the problem is and appears to reset the alarm.......Does anyone have any ideas?

And if I buy another Alarm ECU unit off ebay etc these are obviously second hand can you get new ones or reconditioned ones, as there is no guarantee that after spend £45+ that will work or for how long??

Thanks