How to tell if I have a factory alarm

I have a 1990 535i, how can I tell if I have a factory alarm? I read the owners manual and it says there's a blinking light on to of the dash and that it is set when you double lock the doors. I don't see any
alarm light so I'm guessing mine doesn't have it. But to me this seems like somthing that would be standard equiptment on a car like the 535.
Did only some come with an alarm, how can I tell?
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Open boot, put stone on light switch, leave boot open, deadlock car, wait ~1 minute, remove stone. Deafening noise -> alarm, nothing -> no alarm or it is not working.
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