Sensatronics E4 looks like a good option, exactly what do we need?

The Sensatronics E4 is a simple temperature only monitor. It has a built-in web server so that you can view temperatures remotely. In order to set up thresholds and alerts via email, the E4 integrates with any SNMP based network monitor (you may already have something or we recommend Intellipool). You will also require at least one temperature probe, and obviously a network to connect it to!