The device is found by the keywords “Dakota Weather Station Clip”. It has a battery holder for a coin cell, which can be opened/closed with one such cell (or a fingernail unless it's too tight). It's convenient but adds thickness to the device, most commonly a bike speedometer. It is featured on Wikipedia's list of screw head types (linked by OP) although most such covers don't actually screw in, they latch after a small rotation. This seems to be one of them since there's a triangle marking the latch position (albeit useless without a corresponding label on the device).  I've seen ones where the clip has been clearly forced with a small flathead screwdriver. If you have one (or a piece of cutlery, ballpoint pen core, twig or something), insert it sideways instead for more torque without damaging force!