Good Afternoon. I can tell you that my favourite monitoring tool for a datacenter is extremely basic and does not give me any features I dont need.
I have used a product from Sensaphone before. Instead of e-mailing you, it will actually call you with the status of the server room. You can also call it at anytime to get an update on the status of your server room. I find e-mail alerts are somewhat pointless unless you have 24x7 staffing to read emails or you are checking e-mails frequently.
It used to call me and say "Temperature 1 is high" then it would give me the temperature readings for all my zones. The noise monitoring sneaks up on you, so you have to be careful! The buzzer for our fire alarm was somewhat near the unit and it called me and said "Sound level is high, listen to the sound for 10 seconds" that is all the warning it gives...then it opens the mic and you have to quickly pull the phone away from your ear.
The best feature of this device is that the basic model with 4 sensor inputs is only $395 (List MSRP).
Sensaphone - Model 400 Basic Monitoring
If you froogle it, you can find them for ~ $355
Good Luck!