Small dual action switch; so touching it counts as a “half press” and applying pressure a full click.  As used for camera shutters where a half press activates the systems and triggers the auto focus system etc.

In this case it's built around a 5mm TACT switch, two strips of adhesive backed copper tape, a tiny piece of conductive foam (small microprocessors normally come with it), and an M3 bolt.

Measure the resistance between he two copper strips and when pressure is applied; enough to squish the foam but not enough to click the tact switch; the resistance should drop from Mohms to a few thousand.