The simplicity of this 3D printed device is wonderful – the camera fits into the housing, held in by the tripod screw; and a lever arrangement physically pushs the button on the pull of a string. Easy to rig, and simple to use. They even include a matching ring to put on the end of the string.
There is another, cheaper, device out there, but it requires being stuck to your camera with adhesive pads. I far prefer this non-permanent solution.