Comment by alentred

With respect, this misses some important constraints. Scale it to thousands of locations and target 99% SLA. Now you have a maintenance problem in remote physical places, requirements for hardware reliability, subcontractors to manage, need a reliable network connectivity, etc. You also need to collect and redistribute the data (API or whatever) - while this is a trivial problem today, still you incur costs for hosting, network, etc. While I actually agree with the sentiment, it is not just a $3 sensor either.