When I first run locally-built software I tend to notice XProtect scanning each binary when it is launched. I know that XProtect matches the executable against a pre-downloaded list of malware signatures rather than sending data to the internet, but I haven't monitored network traffic to be sure it is purely local. You can see the malware signatures it uses at /private/var/protected/xprotect/XProtect.bundle/Contents/Resources/XProtect.yara if you're curious.

> phones home

Nope.

It has a built in malware scanner, but that just requires a downloaded list of known malware signatures.