Measure the ambient temperature or outside temperature acquired by your local meteorological station*.
If features real thermometer look with analog and digital readout, Celsius and Fahrenheit scale and Indoor / Outdoor option.
It also has an animated weather background option based on the current weather conditions outside.
NOTE: Thermometer can measure and display the ambient temperature in which your device is, however very few devices have dedicated ambient temperature sensor so on most devices the measured and displayed temperature is the temperature of the device's internal electronics or battery and this is the same to the actual ambient temperature only if the device was long time on stand-by so the only correct way to know the actual ambient temperature is to start this app right after you wake your device that has been sitting on standby for at least an hour.
This limitation is not app's fault and by using this method you can measure the actual ambient temperature to an accuracy of a degree.
*Outdoor temperature and weather information is provided by the Meteorologisk institutt of Norway NRK weather web service.