I setup a 2GB / 2 CPU Core Droplet in NY 3, then created a CPU Load alert for usage over 5% for 5 minutes for this test. It didn't work as I had expected, so this may be something you might want to create a ticket on.
For this test, I used
stress which was installed using
apt -y install stress and first ran using:
stress --cpu 1
The load shot up to 1.0 and I allowed it to run for 7 minutes -- the load increased slightly between the 5 and 7 minute mark -- I never received an alert, even though 1.0 is definitely more than 5%.
Since this is a multi-core Droplet, I upped the CPU count for
stress and used:
stress --cpu 2
That seems to have worked as the load shot up well past 1.0 and not long after, an alert was send out stating that I was using ~70% of my available CPU.
So when it comes to CPU usage, cores seem to matter in the stress test. The alerts do not seem to fire off if you're only using 1 CPU core out of multiple, thus you'd have to effectively be using a threaded test or application to trigger the alerts.
I'm not sure if this is by design as this is the first time I've used the alerts, but I would recommend putting a ticket in to see if this is the norm.