I bought it mainly for the car clock because mine broke. It's quite nice and fits very well where I put it! It only works with batteries and connects to the cigarette lighter only for the light! I cut the plug for the cigarette lighter and connected it with the fuse of the old clock, so when I turn on the engine, it lights up too! That way, during the day, the lighting doesn't work! The lighting comes in two colors, blue and orange, which change with the switch it has!
It also has a voltmeter to measure the battery, but it only works when it's connected to power (logical).
The external temperature measurements were made by comparing it with a meteorological station I have at home, and it is very accurate, with differences of half a degree, because this one doesn't have decimal numbers.
I placed the sensor underneath (not inside) the driver's side mirror in the middle, as it is the only place where I get the correct temperature. I tried it (in many cars I had before) in various points of the car, but it only showed the correct temperature on the mirror. Of course, the thermometer also plays a role, and this one is good.
I gave it four stars because when I put it into operation, it kept turning on and off continuously and resetting. I fixed it by placing a small piece of hard paper in the battery compartment cover, which presses the batteries and keeps them from moving, and now it works perfectly. I have tried several similar products over time, and this one seems reliable in all aspects so far! I would recommend it for purchase because it seems good. Of course, time will tell its durability.
Also, a piece of advice: if you leave the car in the sun, cover it with something because the sun darkens the screen and gradually damages it.