I'd appreciate comment on whether I understand the limitations with MQTT and low power. Using deep sleep the ESP12 consumes microamps and my sensor is insignificant. The big drain on the battery is WiFi. Sending an MQTT message is taking around 10ms which seems at first sight promising. Unfortunately it looks to me like deep sleep ends the connection, and reconnection takes 4 or more seconds. I'd thought that deep sleep, static IP, and MQTT were the way to get very low power consumption but it looks to me like they don't solve the problem. MQTT on ESP12 with battery power and static IP How often are you planning to make a connection and send data? That depends on the power consumption of each connection. Ideally 16s but I know that's not feasible unless time to connect is way less than I'm seeing. I calculate I can get 60 connections in 24 hours if I run off 2xAA Lithium and want them to last over 6 months. I discovered the ESP32-S2 a couple of days ago and it seems to be have a sleep mode that sends a beacon and averages 24uA. So that looks my best hope unless I can get the start up and MQTT connect well below 4 seconds. mqtt deep sleep static ip esp8266
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