As it says on the box.
I’m usually lax in remembering when buzz words first appeared so bear with me.
I first noticed the preponderence of the word " tech " in Dollhouse, but I know its use predates the Whedonverse.
First use in its current form?
Tech has had a lot of uses. From etymonline.com:
Yes, what do you mean by tech? Technology? Technician? Technical? Something else?
What I mean is its use as a piece of equipment.
e.g. " This piece of alien tech completely baffles me! ".
In that case it’s just a contraction of technology, and dates from 1859 as per Exapno Mapcase’s reference.
If you want a specific reference where somebody used it as a synonym for “piece of equipment”, that’s going to be hard to track down. It was certainly common enough by the late 80s for it to be used regularly in science fiction writing.