Use ESP NOW to monitor a remote battery powered sensor
GoNotify Slave ===> GoNotify Master ===> Wifi AP Sensor Bridge espnow controller to MQTT Internet connectivity
To compile Arduino sketches with esp now code do the following: Quit Arduino IDE and edit this file: C:\Users<username>\AppData\Local\Arduino15\packages\esp8266\hardware\esp8266<esp8266 version>\platform.txt
Search "compiler.c.elf.libs", and append "-lespnow" at the end of the line. Then you can build it by Arduino IDE.