The "heartbeat sensor" was actually an item in the Rainbow Six FPS, too.
They were still a good read though.
Yeah, according to this wiki citation[0], the tie-ins were a bit ad-hoc but the game plot was actually finalized before the book was done, which accounts for the discrepancies. So there's no real way of knowing what started out as a game mechanic.
Worked out better than Splinter Cell, anyway-- I don't think I got through more than a page of the novelization. (Which wasn't written by Clancy, FWIW.)
[0] https://web.archive.org/web/20010804114957/http://gamasutra....
Maybe I gave him too little credit in this case. Either he was familiar with prototype tech that we aren't aware of yet, or he was actually a decent near-future sci-fi writer.