Turning the System Off (2/2)

Another option is the attiny-10 ($0.3, 50ua @ 128kHz, 5V)
More size efficient, less power efficient

It can run at 5V and turn on/off the 3V3 for the "real" system.
And (like the 202 in prev. page) it can communicate with the "big" uC

But, most importantly,
    the main uC must be able
    to flash this auxiliary uC.