Both men try to saw through their chains, but Adam's saw breaks. Gordon realizes the saws are intended for their feet, and identifies their captor as the Jigsaw Killer, a serial killer who tests his victims' will to survive through murderous contraptions known as "games", whom Gordon knows about because he was once a suspect.

Idk if this was in the movie as I didn't watch it. But if the thing they're attached to us hardened steel a hacksaw wouldn't have a chance of going through it. It would wear the teeth right off.

i mean you're dealing with a mass murderer who thinks of himself as justice incarnate. if you don't play along a bit at least you're probably just going to be redrugged and put in a worse trap

But also, earlier in the movie, he had to take off his shirt to reach the cassette tape. And this time, to reach the keys he…saws off his own foot.