We’re all familiar with digital, stand-alone thermometers. They’re compact and accurate and the sensors they use are tiny. So why don’t our smartphones, these tech-swiss-army-knives, have this handy feature?

Why smartphones don’t have thermometers?

Of course, smartphones are infinitely more complex and capable than a basic digital thermometer. The issue here is not that manufacturers can’t fit yet another sensor. In fact, smartphones have multiple thermosensors already. They’re used to measure the temperatures of the battery and the chips, preventing disaster in case something goes wrong. But measuring ambient temperature from a device that’s constantly going through periods of heating up and cooling down is tricky business. And by tricky, we mean almost impossible to do accurately. Obviously, the sensor should be somewhere on the outside of the phone. But a smartphone thermometer can’t be sticking out because that would be ugly. So it has to be embedded in the frame or the back of the device.

But these same parts are generally used to dump heat from the internal components, or in other words, as a basic passive radiator. Essentially, manufacturers would have to put a thermometer on a radiator and still provide measurements that make sense for the user.

There are ways to mitigate the influence of the device’s own temperature. Using the data from the internal sensors and clever algorithms, you can end up with a number that is closer to the real ambient temperature than if you were solely relying on the thermometer. Still, “closer” is not exactly good enough, it’s basically another word for “best guess”, and if that’s all the phone will provide, you might as well guess yourself.

Smartphones with thermometers do exist

The idea is nothing new and manufacturers in their constant pursuit of innovation did give it a try. Namely, Samsung and Motorola had phones with thermometers. Samsung did it with the Galaxy S4 and Note 3. According to the instructions for using this feature, measuring the temperature required you to leave the device to cool off from any heat it might have accumulated during use and leave it somewhere so it doesn’t get warm from your hands.

As you might imagine, it’s far from practical and even after following the instructions, the accuracy of the measurements was doubtful. That’s probably why Samsung promptly dropped the idea and never tried it again.

Don’t trust thermometer apps

Lack of accuracy has never stopped app developers, however. Just like all the shady blood-pressure-measuring apps we’ve talked about before, there are hundreds of apps that say they’ll turn your phone into a thermometer. And show you as many ads as possible while showing you a guesstimate of the ambient temperature.

So, while our phones can do a lot, as long as they’re a thermal roller coaster, we won’t be getting any useful ambient temperature readings from them.