A year ago I successfully managed, with the help gathered here, to add an Eliwell IDPlus 961 Controller to my Husky Beer cooler and make a suitable environment for my reptile's hibernation; this environment is stable (+/- 1C) at around 5C which is perfect.

However, I would like to now add a fail safe... so that if the electronics were to fail in an always ON mode, such that the fridge were to never get sub-zero (0C) as this would mean certain death to the inhabitants.

Please could you point me at a cheap device that would 'trip' at a setting of 0C and subsequently just sit in alarm (audible) at that point indicating a malfunction; this would then just go in series with the power supply.

Thanks
BfW