This is a great Temperature Monitoring system which I’d like to share with you here.
The total cost is about USD30. Cheap, but functional.
It’s based on Arduino Mega 2560.The working voltage of this system is DC5V. It can measure the current temperature, humidity and smoke. It can display real-time data by the 1602 LCD and can realize the sound and light alarm when in the dangerous temperature and humidity. It is a simply and easily to operate monitoring alarm system about temperature humidity and smoke.
Here is the hyperlink of this project: http://www.instructables.com/id/DIY-Temperature-Humidity-Smoke-Detector-Alarm-Syst/