Firewall Guard Pro

Firewall Guard Pro protects your Mac by watching over who connects to your network. In addition, it monitors your computer for any suspicious activity.

The tool constantly scans your network and notifies you when a device is connecting to it. So if a hacker tries to connect, you'll know. The program also shields your Mac from man-in-the-middle (MitM) hacking, where the attacker is able to intercept, modify, and even stop your network traffic.