An earlier post, Managing channels, ends with the observation that "perhaps there should be monitoring in place, so that if no readings have come in during some period of time the pico's owner could be notified by text or email." This recently became an issue because of a different failure mode with a similar symptom.
In the earlier case, an error in managing channels made it so that no temperatures were recorded for hours on end. A few days ago, just one of the sensors stopped sending temperatures for several hours before this was noticed and days before someone could go on-site to reset it.
This post will show how to watch for the situation where readings are not received from one or more sensors for over an hour. It is easy to react to an event, but harder to react to something not happening.
We are going to layer on a ruleset that will send an email message to the pico's owner when it notices that expected readings have not arrived.
