Is there Brown-out detection for Arduino Uno?

[MarkT]

The brown-out detector can be set for 1.8, 2.7 or 4.3V via the extended fuse byte. Arduino Unos are set for the 2.7V level. I'm currently working on a project where it was beneficial to change it to 4.3V.

Isn't 2.7V a bit low? At 16 MHz the processor requires 3.78V. So it would become unreliable before the brown-out reset kicked in.

True, but 4.3V was probably deemed to close for comfort for general use (Arduino's can run off 3 alkaline cells nicely, which is
4.5V...)

At room temperature it seems you can run a 328 or 168 Arduino at 3.3V and 16MHz reliably, its at higher termperatures that it will
actually fail (the graph in the datasheet doesn't give temperature dependence though, this is anecdotal data only, but CMOS is
faster at lower temperatures).