Joe Carnahan had been trying to make this movie for years. It was originally called "Continue" and was written by Chris Borey and Eddie Borey in 2010. Carnahan rewrote the script and announced in 2012 that he would direct it for 20th Century Fox. He later filmed a screen test with Frank Grillo and posted it online. Fox ultimately decided not to move forward with it.
No no no! God damn!
Roy Pulver: Don't worry, Dave, it'll grow back.
When Roy extracts the tracker from his tooth and shows him to Dave, the tracking device has an LED that's flashing. While it is understandable that this might be done to make this plot device clearer to see for the viewers, it is very silly to have a blinking light on an implantable tracker. The light would serve no use, and LED lights consume an awful lot of energy.