Since you mention Reddit already /r/arduino is sometimes useful - though often it is a case of the blind leading the blind. For most of my projects I prefer t

Since you mention Reddit already /r/arduino is sometimes useful - though often it is a case of the blind leading the blind. For most of my projects I prefer to use ESP8266 devices, since they're cheaper than (official) arduino boards and feature onboard WiFi. For that /r/esp8266 is a good resource. Mostly though designing a simple sensor/and monitor simple. The hard part is making it fool-proof, user-friendly, and easy to mass-market. Assembling 20 devices by hand is simple, but you don't want to be doing it for 100+!