This myth is propagated by dramatic movie scenes where survivors buried under rubble, as well as criminals hiding inside dark buildings, are caught by thermal cameras from the outside.

To understand what material thermal imagers can or cannot ‘see’ through, it is important to understand the concept of emissivity. This is a measure of how well substances transmit heat through them, not only by direct contact, but also by radiation of infrared waves.

Walls made of stone and bricks have a poor emissi­vity overall, and therefore thermal imagers are gene­rally not able to ‘see’ through them. This is unless the temperature inside is so high it causes the entire wall to heat up, such as caused by a large fire. Such movie scenes as described above, therefore, cannot be considered at all realistic: one cannot see through walls using thermal imaging.