I can't believe no ones commented on my "Cut the extension cord with the trimmer" comment.... Maybe it's more common an occurrence than I think.
Since my freezer too is in the garage, the wife and I both make a habit of checking the light every time we go by it - so hopefully it would never be more than 12 hours without power - but I don't know how long everything will stay frozen.
E, looking forward to the photresitor tutorial. I already have CAT 5 running into the garage for my garage door sensor (2 wires) and remote door trigger (2 wires) leaving me 4 wires to do other stuff with - like monitor the freezer.
Why couldn't you use something like THIS, tape it on the outside of the cord going to the freezer (don't have to cut in the cord as its an inductive pickup), then use electron's HOW TO for monitoring the light?
This wouldn't of course measure temperature but would be a method of determining if AC was present (still plugged in and power applied to freezer).
How bout a standard thermostat electrically connected to a RF motion sensor (to detect voltage, not motion hack applied) that is all mounted IN the freezer? So, when the temp goes to a setpoint, the "motion" sensor triggers the RF to turn a HS device ON which triggers warning events.
Problem would be mounting the temp sense device as most are mercury switch which requires a certain orientation.
Just keep in mind that after a power outage, it will stay very cold for several hours (I doubt the temperature would change much), so if you aren't monitoring the power as well, it might be too late (or cost too much energy rather) when you get notified that there was a temperature increase as it will take a while to bring the freezer back to its regular temperature.
I would agree with Dan that it would be wise to monitor both the power and temp. I can see it being powered up and the freezer not cooling so going with the temp monitoring is wise, but also if power goes out you want to notified right away so you can quickly remedy the situation.
Monitoring your freezer power is especially what you want, if you loose your house power, then being notified of freezer problems would be useless. But if you (or your wife) trigger the circuit breaker because you plugged in a new device which has electrical problems, or the freezer mechanically dies, then you definitely want to know about this. I agree that temperature monitoring is a must if you can do it, but don't think monitoring power is a waste of resources.
Its magnet wire. We use it at work all the time and it works like a charm. Its as thin as a piece of hair and is actually electrically insulated. When you want to make an electrical connection you have to scape off the outer coating befor you solder.