He was very tech oriented and worked extensively with people in the field to try to make his novels sound as accurate on the details as he could.
...with the glaring and amazingly stupid exception of the physically implausible "life signs detector" in Rainbow Six. In fact, the whole Rainbow Six book felt a bit weird, even though the plot was cool. The Brain Eater must have gotten him too in the end, it seems.
I did find myself wondering, when I read the book, whether the idea for creating this magical device was just a means of justifying / explaining the "radar" type display that was in the game released around the same time (Hey, guys... how are we going to explain how in the game we're making you'll know the exact location and orientation of enemies and hostages we can't even see? Oh, we'll just conjure a magical doodad that can detect a human heartbeat through walls! Great!).
Since the two were in development at the same time, I figured that this would be a possible explanation for why Clancy's near-habitual technical plausibility seemed to be taking the month off when this device found its way into the books. It's just a guess on my part, though. I guess we'll never know now (unless someone at either the game or the book's publishers fess up to the conversation happening)!