When you're using a smoker, one of the most difficult things to do is keep track of temperature. Not only do you have to worry about the chamber temperature, but you also have to worry about the internal temperature of whatever you're cooking. Lifting the lid to check on that is only going to make the cook time longer, as well as letting out all the smoke... not to mention the fact that you have to go outside to do it.
All these things seem like petty things to worry about when you're making delicious food, but when you're cooking something for 8 hours or more, you'd be happy to have something that would make your life a little easier.
To this day, I haven't found a better solution than the Maverick Smoker Thermometer. Not only does it monitor both temperatures, but it does it from inside your house with its remote receiver. I love to constantly monitor those long smokes, and this gives me the ability to do it without having to constantly hover over the smoker, which is a great thing indeed.
The waterproof remote transmitter has two probes, one that mounts to the cooking grate (with a supplied bracket) to monitor chamber temperature, and another food probe that is inserted into the meat. Last year I smoked a brisket for about 12 hours in a rainstorm with 20mph winds. This was for a competition or I would have avoided cooking on this day entirely. Although it sounds annoying, I was inside for the vast majority of the time and only had to go out to make some minor adjustments and add fuel very occasionally. It really made the experience a lot more tolerable. Even going outside every half hour to check my temps would have been a huge ordeal.
I'm not sure what the maximum range is, but it had no trouble making it the 60 feet into my apartment with fresh AAA batteries (supplied!), and the fact that the transmitter even has a cycling display was a big bonus. That way the receiver can live inside the kitchen, and when I walk by the smoker on the way to do something else I can check up on the progress without having to be near the other unit.
A small transmitter icon on the receiver lets you know if you're out of range, and the temperature of the meat probe seems reasonably accurate (within 3 degrees of my instant read). Setup is a breeze, just turn the transmitter on first and then the receiver to synchronize them. The entire system retails for under $40 from most places, and is available at Fred's Music and BBQ Supply locally, as well as Amazon and other online retailers. Remember, if you're lookin', you aint cookin'.