You can use a thermometer app on your iOS or Android device to measure temperature, but if you want a more tactile way or need more accurate data, the Thermodo tiny thermometer may be more suitable for you.
Thermodo is a portable and practical thermometer designed to offer you an easy way to measure temperature via your Android or iOS devices. As we can see from the images, the thermometer features ultra compact design, and has an integrated 3.5mm connector in order that you can easily plug the tiny thermometer into the 3.5mm audio jack on your smartphone, and using existed iPhone apps like Thermo and Haze or its companion app under development you can conveniently check and record the temperatures from the thermometer, and its open source SDK will bring more applications for Mac, Android, Arduino, Raspberry Pi and more. Apart from that, using the attached key ring you can always have the thermometer with you.
At present the team of Thermodo is raising fund at Kickstarter. Pledging $25 will let you own the tiny thermometer. If you’re interested, jump to Kickstarter official site for more details.