Assuming I am using Skydemon on a mobile device providing GPS altitude. GPS altitude should roughly correspond to Altitude (QNH). How does SkyDemon work out what Flight Level I'm at to warn me of airspace that's defined in terms of FL? Is it worked out automatically based on QNH information from downloaded METARS?

No, SkyDemon does not currently attempt any kind of pressure-based calculations to change FL to actual altitude before issuing warnings. FL75 always evaluates to 7500 feet.

Thanks Tim. I think it would be quite valuable to correct FL properly based on the regional pressure, if we are to rely on airspace warnings from SD in flight...
(especially as I have now started to use SD in a glider due to its superior airspace and NOTAM depiction!)