I thought there already was a thread about this on the forum, but they seem to either be outdated or incomplete.
The article on the official docs only describes how to set up SSH tunneling (which is safer), but that is not what you asked for.
Before I start I have to just mention the disclaimer if anyone else that you read this.
Doing this opens up your computer to security vulnerabilities over your local network. Do not attempt this unless you are ready to accept the risk.
Install activitywatch as usual, then go to the aw-server config file, it’s location is platform dependent and is documented here: Directories
Then, make sure that the computer has its firewall either turned off, or allows the port 5600.
open the aw-server.toml file, and change the IP to 0.0.0.0 to bind the port to be exposed outside of localhost, and then restart aw-server.
You might also have to change some cors_origin settings in aw-server too depending on your browser. Was a while since I tried this so I don’t remember exactly.