[vacri]

Simple if you already have Nagios set up and running... far from simple if you haven't.

Though someone here posted a video a couple of years ago where the speaker was imploring "Stop using Nagios [it's terrible]". At the end, someone asked him what they should use instead, to which the speaker didn't have an answer (his tool that he was speaking about was still in development)

Edit: but yes, you're right in that the important thing is that the tool will alert you without you having to remember to check it.