Whether you’re grilling over gas or charcoal, the very best way to know if your grilled food is cooked to a safe internal temperature, as well as to your preferred doneness, is to test it with an accurate thermometer. Rely on this thermometer for assurance that you’ve turned out perfectly grilled food every time you barbecue.
I cook steak and chicken outside on the grill quite often. I prefer not to cut the meat open to check for done-ness. It lets the juice out and also looks dumb when you serve it. With this I just poke it, wait a few seconds then check for temp. Steak at 125 and chicken at 175. This is great.