I mean, you could just put in a few more heat sensors.

But the dryer knowing that it, and most of your possessions, are about to cease to exist isn't really useful information. It doesn't remove the obligation that it be supervised. Dryer fires start quickly, often due to lint build-up, and can start when the dryer is operating in its normal temperature regime. Thus the sensors would often only be helpful in identifying that a fire has started, not in preventing it. Thus, unless the dryer has some way of intervening in the fire (like my admittedly sarcastic halon system), its "smart"ness isn't valuable for this failure mode.

> Dryer fires start quickly, often due to lint build-up, and can start when the dryer is operating in its normal temperature regime.

Lint does not catch fire at 140F.

You seem to have very strong opinions about this issue. I'm not convinced they are well-supported by either experience or data.

"Task 4. Determine Characteristics Required for Lint Ignition

Lint that accumulates on the heater housing can easily ignite under conditions of a failed high-limit thermostat and a blocked exhaust vent. Lint accumulating near the heater intake can ignite before the high-limit thermostat switches the heater element off. Lint ingested by the heater and embers expelled from the heater outlet can easily ignite additional lint or fabric in the air stream, resulting in additional embers in the dryer system and exhaust vent."

Source: https://www.cpsc.gov/PageFiles/117075/dryer.pdf

Oh, looks like the top result for dryer temperature was just wrong. And the various numbers I'm seeing for what temperatures are dangerous for lint are wildly inconsistent.

But I can say for sure that those tested dryers are getting much hotter than necessary. Look at the designs on page 6 and 7. Small heater boxes with thin hot coils. If you redesigned it as a big block of heatsink fins with the heating element buried inside, you'd be a lot further away from causing ignition. It would cost more, but in a sub-$100 way.

So I'm unsure at this point. I don't have the resources to test exactly what temperatures are necessary and safe, and which one is higher.

Welcome to the science of fire. If you pump energy into a system faster than you are removing it then you are heating it up, if you pump energy out faster than you are adding it then you are cooling something down.

This is how hay bales that are a little moist will catch fire, the digestive process (which is slow but exothermal) of the bacteria in the center of the slightly rotting bale of hay are so well insulated from the outside world by the rest of the hay that the temperature will at some point exceed the ignition temperature of the hay and then you have spontaneous combustion.

Something very similar can happy to driers if the exit ducts become more clogged than a certain percentage.

And let's not even talk about gas fired dryers (does anybody still use those other than dry cleaning services?).

> Welcome to the science of fire. If you pump energy into a system faster than you are removing it then you are heating it up, if you pump energy out faster than you are adding it then you are cooling something down.

That's why I said "more temperature sensors". It's possible to design a relatively-standard dryer where no part ever gets above boiling, even when the output is completely blocked, giving you a huge margin of error.

Heat in a dryer is all externally applied. It can't build up on its own.

I have had gas dryers whenever I've had a house with gas service. They dry faster and cost a lot less to operate.

> Lint does not catch fire at 140F.

No but sparks that can ignite lint are common risks around operating dryers (both wiring faults and static discharges are issues.)