Pyroelectric sensor has each pixel's secondary electrode made with no contact with other secondary electrodes. The pyroelectric sensor consists of a series of pixels (12A) with primary (14) and secondary (28) electrodes on opposite surfaces of a thin porous pyroelectric layer (20A) on a substrate (8A). The secondary electrode of each pixel has either no metallic contact with other secondary electrodes or a contact only via a metal track of relatively thin section. The pyroelectric layer is applied by a sol-gel procedure with the aid of a soluble polymer in a base solution, and the substrate incorporates an intermediate layer (32) of an aerogel providing thermal insulation between the pixels and substrate.