We also have a need for this sort of thing, and I was asked by
support to raise it here as a feature request.
In our case we would need different types of alerts depending
on threshold value and with different contacts - Warnings and Critical
Alerts would be enough.
The best example I can think of is with Hard Drive usage
thresholds. A warning would be sent to the whole team when usage
reaches a certain point -say, 80% of HDD capacity , so the team can
react and clear space before there is an issue.
And then have another type of alert when the issue is critical
(95% of HDD capacity) - with the possibility to send it to a different
recipient (the on-call team) to treat it as a critical issue.
I've looked into escalations, which would help a little,
but apparently they don't work for 'trouble', only
'down' status monitors.