Mostly the latter, but we can try to provide a few more examples and guidelines! laser weapons, hologram projectors, scanning devices from X-rays to spectrography and back, solar-charged heat swords, hypnotic mirrors, time pieces that can measure everything from heartbeat to orbital resonance...

As far as knowledge of how to build them, that's doable, but without proper materials and tools it would be tough. We're not inclined to forbid, though, just to let you know a little more in-depth effort might be involved to produce such things.