Monitor WIFI Hackers

Are there any tools to monitor attacks on a WIFI modem with the primary goal of stealing bandwidth.
Also, is there any "forensic" procedure to identify hackers?
Appreciate any advice.

Firstly Yes, they are called intrusion detection tools, they basically monitors network and/or system activities and alert you of possible intruders. Tools like
AirSnare do it quite well.

You could also use a tool like Nmap and identify all computer within your network, any computer IP address you do not know would be considered an intruder. However, saying that, it is probably better to have a look at your network security in general and ask yourself why an IDS/IPS is necessary in the first place.

Are you concerned about people trying to break into your Wi-Fi locally? If so, what kind of Security measures do you already have in place to prevent people from gaining access? This would need to be evaluated first.

In relation to a procedure of some sorts, there is a methodology to hacking, and in turn, ways to prevent it , something like that it probably a topic too large to cover in one post, and at this point, unnecessary ( unless thats something your interested in and would like more information ).

However you can read something like Wireless Hacking Techniques. It gives you an idea of the methods that hackers use to gain access to Wi-Fi and, as you can see, goes into a bit of detail. And thats just the tip of the Iceberg so to speak.

I agree with richnrockville. If you have an older router that uses WEP (Wired Equivalent Privacy) and does not support WPA or WPA2 (Wi‑Fi Protected Access), I strongly suggest replacing it with a new router. WEP security is relatively easy to crack and routers are not that expensive. You don't want this to happen -- Insecure Wi-Fi Results in Police Raid.