This device works well. I have it attached to the side of my garage refrigerator via the magnets on the back of it. I put the sensor on the end of the cord inside the refrigerator.It requires one AAA battery (not included). I really had to struggle to get the battery door off to install it, but with perseverance and the help of a screwdriver, I was finally successful.The temperature can be measured in either C or F via a button on the back. You can also switch between the temperature readings via the sensor (outside) or the temperature via the unit itself (inside). I wish it would have a feature that would automatically go back and forth alternating between the two readings, but it will only constantly stay on whichever one you select.It does come with instructions, but they’re pretty sparse.It seems to be fairly accurate. I compared it with another thermometer that I have inside the refrigerator, and they were one degree apart. I discovered that I needed to adjust the temperature control to slightly lower the temperature to get it under 40 degrees F.I’m fairly pleased with it overall. I like to be able to quickly see how well my refrigerator is working as well as how hot my garage gets in the summer.