I've made two changes to the car today, and now the alarm goes off every time about 10-15 seconds after I arm it.

I just installed my prosport gauges and pod into my newer STI - I'd previously installed them in my old WRX without any issues.

However, since moving my old stereo into the new car, the radio wasn't working, and on searching I found that this was because the later models have an amplifier for the antennae in the rear screen and need power for it.
So I connect the power antennae connector from the stereo harness and hey presto it all works.

The gauges I did as before on my bug WRX - remove the clock pod, cut the wiring to the block that connected it, and then used the blue cable for positive battery, yellow and green for acc and black for negative.
Gauges all came on fine and persist their state (e.g. the startup beeps go after I disable them on first power on).

Has anyone had a similar problem with their blob STI?
It's a Euro car, but has a Sigma alarm (almost identical to the factory fit Subaru one); I was wondering if this is a current drain issue after connecting either the stereo antennae power OR the gauges, but as the gauges didn't cause a problem on my WRX I'm wondering if this is a antennae related issue?