The name is very broad, for certain domains this is a strength but here it is a bit of a weakness because the domain doesn't suggest what kind of monitoring we are talking about. It is nonetheless a premium domain that is completely generic, memorable, easy to spell and remember, and can even be branded. There are many possibilities and many possible end users.
Personally I would use it for network surveillance. E-reputation services is also another very likely purpose, especially for corporations.
I agree with the other members, this domain belongs in the 5-figure range. Up to mid-$$,$$$ with the right mix of patience and exposure. This is not an absolute ceiling in any way. 6 figures is not completely ruled out but I am not saying you will ever be offered this amount. I think up to mid $$,$$$ is more realistic unless you are prepared to wait for many more years.
Have you ever received unsolicited offers ?