Is there a way to build a feed value that indicates if the input is alive or dead (with certain time threshold)

I have a few separate RPis sending inputs via MQTT. Data comes nicely to EmonCMS but I would like to build a dashboard with green/red traffic light to indicate whether the input is alive or dead. (ie RPi software crashed or alive)

The input view on emoncms essentially shows what you want - each individual input and the age of the last received value as well as a red/yellow/green colorcode. What else do you need that isn’t shown there?

I have python based scripts running 24/7 in all these RPis. They are feeding data with various intervals Some constantly in every second, some only when certain criteria is met.

I know that in the feed list one can see the duration from the last value but what I am looking is an indictor in the dashboard that I can share and view remotely anywhere. This indicator should show traffic lights style in the dashboard or any other similar one.

As an example: One of my value is updated in every 10 secs. Now I would like to set a criteria that if there is no new input in 120 secs there would be an indicator to show it in dashboard that something is wrong like green/red.

Do you want this included in emoncms or hosted separately? One thing that comes to mind is to build this monitoring solution using Node-RED installed on the device where emoncms runs based on your existing MQTT inputs. You could set up flows to compare the last timestamp of incoming data to the expected interval and publish the monitoring result also to MQTT. The MQTT topics could also be picked up by emoncms or processed separately.

I have built a nice dashboard that shows electric network frequency data and several power meters instant power. Frequency is controlling the relays that will switch the power on/off. In one RPi the frequency control is one script and relay switching another scripts. These are working locally and publishing data to local MQTT from where the posting script will capture the data and send it to EmonCMS. Input per your picture above are showing the duration from last value but I would like to get a function that gives output per how long it is from the last input value. When the script will fail there is no input coming anymore so this could not be done calculating the delta time from two inputs updates. It needs to be the way the counter is currently calculating in feed table as second from last value. I know this could be done also outside EmonCMS but I would like to do it in EmonCMS as it already has a counter that calculates the duration from the last input value.

Within the EMONCMS dashboard, the feetime widget will show the latency of a feed as a number.
The isactivefeed widget will display a shape whose colour reflects the latency of a feed.
Will one of these widgets meet your need?