How do I get my almost 3yr old to tell me when he has to go potty?

My son is almost 3. If we take him potty every hour and a half or so he will go peepee and stay dry all day,he even stays dry all night. And if we catch him ready to poop and get him on the potty he will poop on the potty. But he wont come to us to tell us when he has to go or do it on his own. We have tried bribes of all kinds, special treats, encouragement, and even tried to lead by example.I know he will eventually do it in his own time but what can we do to further encourage the final phases of potty training?