My question is a Nodejs newbie question. I would like to somehow detect if a user is accessing my network (Wifi) and I would like to indicate the users presence in my network.

How would I go about identifying the user presence. I'm completely clueless as I was unable to find any library that could help me detect this in Node. Is this even possible? If so could you point me to the appropriate libraries and the approach that I need to use.

If you run a router like a Linksys, etc. that can support DD-WRT, you can flash that firmware and then use either SNMP or web page scraping to get connected clients. There are node.js libraries for SNMP and there are a ton of examples of web page scraping with Node.JS.

Alternatively, you could get really complicated and add in RADIUS authentication to your DD-WRT installation and watch for an authentication event.

Another option, you could send ICMP (Ping) packets to every potential address that your router would acknowledge. e.g. if it's 192.168.1.1 on a 255.255.255.0 subnet, you would have 253 addresses to ping. Of course, the connecting user's machine would have to have ICMP responses turned on (which they typically do by default).

I hope one of these suggestions helps.