How can I determine the duration of a power outage?

We recently had several power outages due to late spring storms. None of the outages lasted long enough to worry about food spoiling, but we were home and knew how long we were without power. This made me wonder:

If I left home for a weekend and came back to the stove/coffee pot/microwave flashing (indicating a power loss), what could I do to determine if it had been out long enough for food to become dangerous in the refrigerator (say four hours)?

If I opened the refrigerator and it stunk, that would be a clear indicator, but food can become dangerous well before that point. I'm looking for answers that I would likely already have around the house to know this or something I could build/buy/whatever in advance that would allow me to know this.

• I've never tried this, but could you call the power company when you get back? Or would their website show recent outages? – BrettFromLA Jun 14 '18 at 15:36
• @BrettFromLA My power company might; they have improved things a bit in the past couple of years, but there are so many power companies, a more generic approach would be nice. – UnhandledExcepSean Jun 15 '18 at 15:54

There are two ways that I use.

I use a battery-powered analog clock (with hands) and another similar electric-powered one plugged into the same circuit as the refrigerator. Synchronize them before you leave.

Any difference in time indicates the duration of the outage since the electric clock will stop while the battery one continues. When/If the power resumes both clocks will still be out-of-sync with each other.

For indicating longer times that might affect the freezer, I put a penny on top of an ice cube. If the penny is still on the surface of cube, the outage was not enough to compromise the freezer temperature.

If both the clocks are out of sync and the penny is at the bottom of the ice-cube tray, the outage was longer than twelve hours.

• I like the low tech idea of the penny and ice cube. As far as the clocks, I would think that would only work if they ran an elapsed time like a stop watch. If the power fails multiple times, the electric clock would only show the time elapsed since the most recent failure. – UnhandledExcepSean Jun 13 '18 at 19:32
• @UnhandledExcepSean No, it's the aggregate total. Think about it. – Stan Jun 13 '18 at 20:40
• aggregate total isn't helpful. 4 outages of 2 hours is safe; an 8 hour outage is not, but the aggregate is the same. If you think that is unrealistic, you obviously were not in my area last weekend :) – UnhandledExcepSean Jun 13 '18 at 21:40
• @UnhandledExcepSean Quite possibly, "4 outages of 2 hours is safe; an 8 hour outage is not…" Wouldn't that depend on the circumstances such as the gaps between them? I find emergencies don't have such regularity, unless it does. Meanwhile, using both techniques (coin & clocks) will give you an exact-to-the-minute duration and a good visual indication of the effects of the outage(s) however temporally distributed—continuously or intermittently. This was your question after all. – Stan Jun 13 '18 at 23:13
• @UnhandledExcepSean Oh, look. There's my bus. Well, I'm sure a person like you will find a much better way than the one that has worked for me for years. I didn't come here to argue, debate, or defend. So long, Felicia. – Stan Jun 14 '18 at 15:43

Set up a webcam and a simple CCTV-style recording, and leave a light on. When you get back, scan through the footage at high speed. If the CCTV rides through the outage, you'll be able to tell when and how long the lights went off. If it doesn't, you'll have at least some idea of when and how long the outage was by looking at the timestamps of the image files.

• I think this would only tell you how much time since the most recent power outage. – UnhandledExcepSean Jun 13 '18 at 17:46
• @UnhandledExcepSean I've changed the answer. Does this help? – Lawrence Jun 13 '18 at 17:55
• Seems like a pretty good solution. – UnhandledExcepSean Jun 13 '18 at 17:58
• @UnhandledExcepSean, "Seems like a good solution." Really? I've worked with video. How do you provide power to record with the recorder over the extended time (a weekend is ~50 hours) that you are away? Where will you find enough "footage" for that uninterrupted recording? Most video media won't last more than eight hours. Battery powered equipment would overheat in extended recording mode. Batteries wouldn't last that long. I suppose you could upload this information to an off-site server if the power for your network was available—Oh, wait, there's no electrical power. : ) Next idea? – Stan Jun 15 '18 at 15:39
• In this particular case, I think a webcam hooked up to laptop could work. If the power was off so long the laptop powered off, the safe fridge time almost certainly elapsed. If the laptop was still running, you could check the footage. I do think this is a good working solution, BUT it is not very lifehack-ish since it requires some decent expenditures. – UnhandledExcepSean Jun 15 '18 at 15:58