Another option: Zabbix.

Sounds like overkill initially, but works fine and can be automated fairly well. Once installed (as a LXC/VM or on a seperats device if you want independent monitoring), you can setup a API acess for monitoring Proxmox (which will monitor all LXCs,etc. automatically) and then add the agent on top to monitor the underlying machine. There are dozens of ways to monitor Zabbix hosts temps, HDDs,etc. available online.

In theory you could also let a zabbixproxy collect all your hosts data (e.g. your Proxmox Host, your switch,etc.) in your network and then send it to a VPS outside your network so you monitor offsite and can be alerted when not at home.