The screen door hit the jam this morning and taking a look I see the lower hinge has pulled out. It's held into the aluminium frame using what appear to be sheet metal screws, and I don't think there's anything behind them on the door side. Here's an image, I'm not sure it's very clear:
If you can make that out, you can see the hinge has pulled away. You'll also note that the current location of the screws is not the originals, so this happened in the past and the previous owner simply made new holes in the middle of the hinge.
I don't think putting another set of screws in another set of holes is the solution, does anyone have other suggestions? Is there some sort of tiny toggle bolt that would work?