Open source sensor platform based on ESP8266 and compatible with MQTT.
This demonstrates how you can use the deep sleep function to save a lot of power between measurements and transmissions.
This is a volume based sensor. It uses a microphone sensor with a digital (on/off) output. It takes the running average of the last x seconds. If the running average is more than 0.5 it sends jsensor/bathroom/volume 1 to the configured MQTT broker. There's a minimum "on" time to prevent rapid oscillation and when it turns off, it will send jsensor/bathroom/volume 0. It's simple to configure. Just specify the WiFi, MQTT and sensor settings in the user_config file.