“The man from Box 500 [UK MI5] proudly announced that the thermal-imaging camera at the rear had detected a pattern of movement. Every morning, he reported, at exactly 08:00, the hostages gathered in the commercial section on the ground floor. An SAS officer tartly pointed out the central heating was timed to go on every morning at that hour: the “hostages” detected by MI5’s machine were radiators warming up."

Excerpt From: The Siege by Ben Macintyre

Very good read.