To check temperature with any smoker I recommend a good Thermometer. The ones I have learned to love are the digital meat thermometers with a probe and a 3 foot metal cable. They run around 15 dollars but are worth their weight in gold in my opinion.
You can push the probe into the thickest part of the meat in whatever you are cooking. The metal cable attached to the probe is flat and easily runs through the door even with it closed or you can run it out of a vent or other opening.
The cable attaches to the monitor which sits on top of the smoker and gives you real-time readings on the temperature of the meat you are cooking. Most of them also have an alarm to alert you when a target temperature (set by you) is reached.
Now they have some that are remote so that the cable attached to a sending unit on top of the smoker. You have the monitor on your wrist or belt and know what the temperature is even if you walk off to do other things around the yard, in the garage or whatever.
These can be purchased at Amazon.com or you may also be able to find them at places like Walmart,Ace Hardware, Lowes, Home Depot, etc..
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TIP: Do not let the metal probe touch any other metal or it will fry the probe and you will have to get a new one. Replacement probes run around 5 dollars but there is shipping cost from the company and the hassle of having to wait for a new one to arrive. As with any tools, just be careful and you should be fine.
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your article would have been of greater value if you would have stated where to place the probe, big difference in a brisket, not hitting a bone, etc