I suppose many historical and fantasy medieval stories could be thought of as techno-thrillers, but I think of Clancy and the like. As Strange Horizons points out, thinking about war and the consequences of technology goes to antiquity. Strange Horizons has a fascinating article on the Victorian techno-thriller.

Tellingly, Francis Bacon raised the issue in his classic The New Atlantis (1626), in which the scientifically-minded, nature-conquering Bensalemites proudly tell the story's narrator that they possess "ordnance and instruments of war and engines of all kinds . . . stronger and more violent than yours are, exceeding your greatest cannons and basilisks [heavy siege cannons]."

It seems that one of the world's great geniuses, da Vinci had such intrigues in mind. He famously added a mistake to each of his war machine designs, presumably to confound the enemy if the drawing got into the wrong hands.