You could also get a relay with both N/O and N/C contacts. Connect the 12 vdc alarm to the N/C contact. So if you power up the system and the relay doesn't switch the alarm sounds.
It will probably sound for a moment as you power up.
BUT, the most reliable way is to attach to the 120 volt (load) side contacts and place an alarm on it. But, you need to step down to 12 volts since a 120 volt alarm is not common and would be like a dock bell at the warehouse!
To simplify matters get MBM and the program called "Shutdown". Set you MBM alarm 8c – 10c higher than you highest load temps and it will sound an ALARM and then Shutdown Now will shut your machine down. This covers you for all overheating causes. Probably cost less than a relay and an alarm too.
I took my relay/pump thingy out of my machine and run the pump 24/7 easier on the Eheim.
IMHO
Jim
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