I'm still running the standard sigma? alarm on my uk my99 impreza..problem is sometimes when i start the engine the alarm goes off until the engine actually fires up and is running. is this normal?

Sigma M30 is the std MY99/00 one. "Sigma Sam" is the man who would help you out. It's not normal, although I've had it beep a couple of times when firing it up and just put it down to a lack of voltage - battery or alternator perhaps.

As ozzy says, the alarm sounding when you are cranking the engine is not normal, although the siren can emit various strange chirps and bleeps when cranking if the battery voltage on the vehicle is dropping excessively low.
When you say the alarm "goes off", are we talking the usual consistant siren sound with the indicators also flashing, or just the strange noises as described from the siren?
SS

occasionally it beeps when i start it up but occasionally it also actually proper goes off, havent noticed the indicators flashing but the alarm does sound with the siren.
I have wondered if its down to battery voltage dropping too low as sometimes i dont drive my scoob for up too a week.
apart from that though i've had no probs with the alarm at all.

I would be very surprised if you were getting a genuine "trigger" (ie siren sounding and indicators flashing) - if you could watch for the indicators next time this occurs.
If the indicators aren't flashing, then when you’re cranking the engine over, the vehicle’s battery voltage is dropping so low that the siren thinks that someone has cut it’s power supply – the beep is the siren’s internal battery kicking in, then it realizes its disarmed anyway and stops sounding.
Unfortunately, the cause is a starter motor drawing too much current or more likely the battery not holding sufficient charge (or a combination of both) –
This usually becomes evident during the colder months or if the vehicle has been stood for sometime as the starter has to work harder to turn the engine over.

You can check the vehicle’s battery voltage by pressing digit “8” on the keypad with the ignition “on”. Then turn the ignition “off” within 5 seconds and count the flashes from the alarm LED. 12 flashes= 12 volt.
Obviously, being electrically operated, if the battery voltage is negligible then this feature will not work. Remember the displayed voltage will drop even further during the increased drain caused by cranking

SS

Cheers Sam, some useful advice there i've definately been thinking along those lines of low battery power as if i leave my car for around 5 days then try starting her she does seem a bit slow to turn over. i'll keep an eye out for the indicators flashing when it does it again, i'm sure they dont go as i'm in my garage and would of noticed the indicators lighting the walls up.

I'll also check the battery voltage check as well when i leave her for a few days again.
thanks mate
Ant.