simpleiothings.com has build a Wifi connected smoke alarm using ESP8266 module:
This tutorial will teach you how to build a Wifi Smoke Alarm Notifier for about $10 dollars. You won’t have to code anything, and you won’t have to solder or buy expensive electronics equipment. Any services you are asked to use will be 100% free. Its that easy. Lets get started!
One of the reasons why IoT devices can be built so easily now is because of the ESP8266 development board. IoT enthusiasts have been excited about the ESP8266 because its a full system on a chip (SoC) that has onboard wifi connectivity that can cost as low as 3 dollars.
ESP8266 DIY Wifi Smoke Alarm Notifier – [Link]