Have you ever asked yourself, do I locked the door? With this app via your smartphone you can answer this question in 10 seconds.
This application is from type server-client. Server is based on arduino and C/C++, and the client is based on JAVA. The android app is used to control ESP8266 remotely through a wifi connection.
The role of a server is played by olimex ESP8266-EVB-BAT
The ESP8266-EVB-BAT is a standard module available online - https://www.olimex.com/Products/IoT/ESP8266-EVB-BAT/open-source-hardware