Last week I quickly prototyped my Arduino DIY Gas sensor which monitors smoke, LPG (liquefied petroleum gas), and CO (carbon monoxide). I used the MQ2 smoke/gas sensor and an Arduino nano with a simple ASK 433mhz transmitter to transmit the values out to any radio receiver.
It was well received on the Adafruit Show and Tell event as well as Lady Ada mentioned it on the following Ask an Engineer show. Here are the videos. Full build video soon with code.