A security device including a surface relief microstructure which, in response to incident radiation, replays a hologram viewable within a viewing zone, the hologram including at least a first holographic image element in an image plane spaced from the surface of the microstructure. The device exhibits at least one further image in a plane spaced from the image plane of the first holographic element. On tilting the device, the first holographic image element exhibits apparent movement relative to the further image, which when expressed in radians, a rate of parallax movement per radian equals the spacing between phones and the product of the rate of movement and the included angle of the viewing zone defining a distance at least 20% of the dimension of the device in the direction of movement of the first holographic image element.