Here is a quick NodeRED flow to check a feed on emoncms.org for inactivity ie. stopped updating. The application I needed this for is to ensure a local hydro system that we are monitoring via GSM 3G connection does not drop offline while we’re still debugging the 3G connectivity.
I’ve set up the flow to check a certain feed on Emoncms.org (defined by feed ID) every 30min, if it has not updated in this time since the last check the flow sends me an email. Tweak the parameters to suit your application.