ESP8266 Light Sleep Mode
For details visit https://efcomputer.net.au/blog/esp826...
Demonstration on how to use ESP8266 in Light Sleep mode. ESP8266 will wake up when triggered by level changes on one of the GPIO.
The practical application for this is you can use it as a Door Bell, when someone press a button, the bell will rang, and you can also trigger MQTT messaging to send message to your phone. This will save some precious battery power.