How / where does he get a gun...
(I haven't found this plot hole mentioned on the forums.)
* SPOILERS *
...after the two of them lock him in cuffs and try to get out (unlocking the door), not long after, the blind guy appears and shoots Alex. Ok, he somehow got loose.
But where did he get the gun? It's the magnum gun, same one (and I guess the only magnum in the house - the other was Beretta) he used earlier. We've seen it in the room where he fought Alex, left on the counter. And after Alex wakes up, Alex eventually locks the dog in the room.
This is a major plot hole. Up until this point, I've considered a movie 8/10 but after this point, it goes only downwards. Overall it's a solid movie and I gave it 7 but it would have been 6 if camera/photography wasn't as good.