Service Bus - detect messages not being consumed.

Hello,

We have a software component that puts messages on a service bus queue. We have another component that consumes those messages.
If the consumer component fails, the messages stay on the queue (indefinitely). I'm trying to configure an alert rule to detect this.

I cannot detect on a certain amount of active messages. During times of heavy load, the queue can contain a lot of active messages without there being a problem. I would have to set the limit very high, so it doesn't trigger falsely. But during low load, when the consumer fails, it would take way too long for the active messages to reach the high limit.

I cannot find a way to work with the age of messages. Is there a proper way to detect this?
I asked this question via an Azure support ticket 3 weeks ago, but got no response whatsoever. Maybe a support ticket is not the way to ask a question, but I expected at least an answer pointing me to another direction.
Kind regards,
 Ben