Like most modern gadgets, freezers offer excellent reliability and problems with them are extremely rare. It is easy to be lulled into a false sense of security by this reliability, because like every other gadget freezers can and do go wrong occasionally.

If the problem is not spotted in time, the likely result is a great deal of wasted food. Unfortunately, unless smoke starts to pour out the back of the freezer, it is unlikely that the problem will be noticed until the food has defrosted and you are confronted with a soggy mess.

This very simple alarm project provides an early warning of problems by sounding an audible alarm if the temperature inside the freezer rises above a preset threshold level. The user is alerted to the fault long before the food has a chance to defrost, and hopefully in time to get the problem fixed before the food is ruined.

The circuit is battery powered and is therefore immune to failure of the mains supply. Although the unit must be left running continuously, the current consumption has been kept to a very low level that ensures each set of batteries has virtually its "shelf" life.