A plot hook used in several episodes of Torchwood was the effect of various kinds of alien or otherwise super-advanced technology falling into human hands.
“This technology has been falling to Earth for centuries.” Henry Van Statten, Dalek
Torchwood One deliberately went out looking for technology to swipe, so it’s been part of the setup from the very beginning.
This allows a “how would this advance affect life?” SF story on a small scale, and with no aliens being directly involved it’s all about people and their motivations.
So look at any implausible bit of tech in isolation. Who might have, who would want it, what would they be willing to do for it? The more useful something is, the more various groups will want it (including the PCs and their superiors, and possibly other official groups).
If this is to be a recurring source of plots, I’d set up where all these things are coming from. The magic shop in Buffy provides a variety of phlebotinum even before Giles takes it over, and Friday The Thirteenth: The Series and Warehouse 13 are both series about artefacts causing trouble.
And Doctor Who has hinted at this before, with a Dalek passing from owner to owner until Henry Van Statten acquires it - this summer!
For such a setup, I’d create a consistent black market in such rare items. Perhaps run by a smuggler, a charming conman who doesn’t know quite as much about the things he finds and sells as he really ought to...
The last decision is what happens to the device at the end of the episode. Players will often want to keep it unless it’s really dangerous to the user or the world in general, and sometimes even then they’ll still be tempted by the power. So consider where or not to let them get their hands on anything too unbalancing. Maybe it takes time to learn to use a dangerous gadget safely, or it has a limited number of uses, or some other way to avoid it coming out every week. Players generally don’t mind missing out on a game-wrecking power, since it’s their game it would wreck.
Example: The Perfect Escape
This week’s artefact allows full-on telepresence - it creates a second version of you, temporarily, out of thin air. The device comes in two parts, the main controller and the “point of origin”. The second piece is pretty small - you could post it in a jiffy bag. So your copy can get into anywhere you can plant it, and act freely for up to an hour or so.
Does the original person have direct control over the copy or not? The first option is more powerful, the second makes for more complications as your copy might get into all sorts of trouble. The copy might know it’s a copy and follow the original’s orders to the letter, or it might get distracted... What if you send your copy out on an errand and it never comes back?
Maybe both options are available, with the latter either while the original sleeps or while both are active - I’d put in a penalty for the latter as it’s the most powerful, to do with the obvious distraction of experiencing two sets of sensory input.
If the copy is independent, does the original gain its memories at the point it vanishes? Maybe yes... unless something goes wrong. What if a copy dies?
So there’s all this to consider even before we decide who has their hands on the device. Just to make it really awkward for our heroes, let’s say it’s an expert thief...
The characters are brought in to solve an apparently impossible art theft, getting past state-of-the-art security to take a priceless piece. A strange energy signature was the only clue, a sign that someone used alien technology to do it.
Skywatch field teams are supposed to hand such items over to HQ, but will they? And if they do, is there a chance they could get it back for a vital use in a later episode, when someone really needs to be in two places at once?