We like tiny cool gadgets and Thermodo is one of them. If you want a compact temperature sensor that you can put on your key chain and take with you anywhere Thermodo is right on the spot. It uses 3.5 millimeter headphone jack that you can plug in into your phone to measure temperature around you. The sensor uses iOS and Andorid apps to display the measured temperature. Thermodo is taking into account the ambient mobile device temperature (check the settings) so no worries about getting inaccurate readings when the phone is hot.
Thermodo uses passive temperature sensor built into a 4-pole audio input so what it does is the thermometer will send an audio signal where the temperature sensor is located for the sensor to assess the signal amplitude (dependent on the current temperature) so the software can pick the attenuation through the phone’s microphone and calculate the actual temperature.