I've also been keeping an eye on Bonnie when he (well, "she" in this case) is in the hallway outside of my office. So if I hear footsteps, but Bonnie doesn't move, then I know it's Chica. Watching that hallway also allows me to watch out for Foxy. I honestly think this is a solid strategy! I also do visual checks, seeing where everyone else is, and making sure that Freddy is where she is supposed to be. What about you?