Someone is online if and only if at least one of their computers is online. Use this tool to indicate your online status.
$ online_status -s [-p <port>] [--pubkey </path/to/pubkey>]
$ online_status -c <server> [-p <port>] [--https] [--privkey </path/to/privkey>]
$ curl <server>[:<port>]/status
If online: ONLINE
, otherwise: OFFLINE