Thermapen is a good back-up, but requires opening the door. Good for grilling, not so much for smoking, other than a double-check of the final temperature if you have doubts as you used it. The best insurance is multiple wired probes, hooked into different controls. I have about six probes on hand. A Maverick, and several inexpensive wired probes from big box stores. Probes can fail if moisture gets in them where they attach to the wire. I would have put 4 probes in that smoke, one in each butt, one in the point and one in the flat. I might be paranoid, but if a probe or two seems out of whack, you can usually figure out from the remaining ones what to trust. You don't have to spend a lot of money on the extra "insurance" probes. The meat is usually a pretty big expense on it's own, so it's worth the investment for extra probes, especially if you have one fail mid-smoke.