How long does a freezer stay frozen when the power goes out?

There are $10 battery operated thermometers on Amazon that give you a min and max recorded temp. That is all you need for safety.

I've handled it for decades.

First thing you do when you get your slab is that you wrap it in two towels, then you fold down the loose edges and pop that in a cooler. Towels towels towels, that's my go-to.

You can handle dry ice with your bare hands -- I have scores of times -- the trick is that contact with pressure (squeezing or weight) is what is going to give you frostbite. Otherwise, I have swiftly moved two pound chunks with bare hands if I were lazy. Any pair of winter or driving gloves is sufficient so long as the fingertips aren't open. Just leather gloves are dandy.

Now, if you're feeling fearful, you can drive with the windows down, but to be honest, carbon dioxide in too high of quantities will invoke a gasping/coughing reflex. You would have plenty of warning. You can verify this by putting a small chunk of dry ice in water, leaning over the cup, and inhaling. You'll cough, and that is the reflex to look far. It isn't shy about making itself known. I have driven around with fifty pounds of dry ice in coolers with no issues.

Now that you've driven home, you can take the dry ice, towels and all, and put one in the freezer, one or two in the fridge. Now, this stuff sublimates, so you won't have water everywhere, but don't worry about pressure building up in the two compartments, you'd have to use straps to hold the doors down tight enough to be an issue. I put the dry ice at the top of each compartment, as a trend.

It'll save your refrigerator's worth full of food.

Note, it doesn't just require an outage to stop the freezer working.

Many modern freezers ironically stop working properly under low (but above freezing) room temperatures encountered in unheated rooms (eg outbuildings, garages, etc) in colder climates.

My wife was convinced the refrigerator was failing so I bought a few sensor tags from wirelesstag.net [1] just to be sure. You can certainly build your own using off-the-shelf IOT devices, but for ~$35 you can have a device that senses temperature, humidity, light levels,and runs for several months off an easily replaced cr2032. Although to be fair you must buy a base sensor station for $39 along with the first tag.

Having said that, it definitely gives me peace of mind knowing that my fridge isn't going out and that I haven't left the door open, either.

Next on the agenda is using my smart home controller to adjust cooling temperature on my window unit based on ambient temperature in my bedroom.

https://store.wirelesstag.net/products/wireless-tag-als

It depends on the thermal mass of the contents, the effectiveness of the insulation, and the external ambient environmental temperature.

In real world use, it also generally depends on (1) how frequently and for how long you open it, and (2) whether it's top-loading (efficient) versus front-loading (inefficient).

Source: My venture custom designed and built a refrigeration circuit with autonomous electronic management from scratch over the last year or so, so have done numerous recent tests in this space. I also visited about 4 different fridge factories in Guangdong and spoke to their engineers, investigated the different available chemical coolants, relevant sensors, etc.