Best type of c# solution

I'm pretty new to c# and could do with some help.  I want to create a solution that simply looks to see if a ProcessID has stopped running.  If it has, it logs the user out.  

Fellow EE members have been helping out with code suggestions (thank you), but I am curious as to what type of solution I should build it in.  I want it to have as small a footprint as possible.  It doesn't need any forms/messages, it is simply loaded, presented with the PID (via a command line argument), and then periodically checks to see if it's still running.  If it isn't, it logs the user out.

But the main point of the question is the lightest way to build it (using c#)