Abstract: Apparatus for protection against undesired thermal transfer comprising a printed circuit board (15), an infrared sensing device (100) electrically connected to the printed circuit board (15) by way of an electrical lead (12), and solid thermally insulating material (18, 20) between the board (15) and the device (100) and protecting that side of the device (100) facing the board (15) from thermal transfer from the board (15) to the device (100). The solid thermally insulating material (18) bounds a passageway (19) in the material (18) through which the lead (12) passes. Advantageously, the in sensing device (100) is in thermal communication with a heat sink (14) and the solid thermally insulating material (20) protects the heat sink (14) also against such thermal transfer from the board (15), i.e. thermal radiation from the board (15) and thermal convection currents induced by the board (15).