get a notification when my machine is pinged
Little Snitch may have the feature you want. It allows you to set up rules on network traffic, both inbound and outbound, mostly for blocking unwanted traffic, but I believe it can perform arbitrary actions such as notification for specific rules and types of traffic like ICMP pings.

There's a trial version that you can use to test.

I have no affiliation with Little Snitch or the company behind it.