Security sheet

The present disclosure is directed towards a security sheet (10) for displaying personal data (11) comprising a plastic substrate (12) comprising first and second outer surfaces (13, 14). A first opaque region (21) extends partially across the plastic substrate (12) between the first and second outer surfaces (13, 14). A first window (50) is at least partially surrounded by the first opaque region (21). A security device (51) comprises a transparent first device region (52) and a second device region (53) formed from a second device insert (55). The first and second device regions (52, 53) have different optical detection characteristics. The security device (51) is arranged in the plastic substrate (12) such that, when viewed in reflected light incident upon the first outer surface (13), at least part of the first device region (52) is visible at least partially around the second device region (53) in the first window (50).