We are using a Wifi enabled Relay to experiment with access control named Yunshan Wifi relay.
To add an extra board in the Arduino IDE, these intructions were useful: http://www.instructables.com/id/Quick-Start-to-Nodemcu-ESP8266-on-Arduino-IDE/
Very useful web page with information: https://ucexperiment.wordpress.com/2016/12/18/yunshan-esp8266-250v-15a-acdc-network-wifi-relay-module/
We first tested with a blinkled example. The Blue LED on the ESP8826 is pin 2.
Then we modified the example to work with MQTT and put the resulting code in the repository "machine access": https://github.com/bitraf/machineaccess