Can be bundled on a low power consumption board (that needs to be on all the time).

There is a good chance that RadioBoard (under desing now) will provide the hardware necessary for these function as well.

There must be some atmega just right for the job:

..... write your thoughts here ....

Atmel has a small board called the butterfly. It has an LCD display and is inexpensive. It would be just the thing for a dashboard display to give time, WB02 display etc.

Actually AtMega128 could be used (think semipopulated AfreshBoard)spending much time in sleepmode, if the other components are careful not to consume much current.

Suggestion: 8 MHz Atmega128L, driven at 4 MHz, mostly sleeping, making his own 3..5 V from the battery with SW-driven switching regulation.

You need a PNP (from VBatt), an NPN (driving the PNP), 2 base resistors, a BE resistor for PNP, an LC and a flyback diode for the switching regulator. Around 100Hz you have enough time to measure and switch the transistors.. Also a 5.1V Zener parallel with C in case you get the program wrong :-)

Note: The atmega ADC can be made to measure it's own supply voltage...

why not have the 5.1V Zener go to the base of a NPN and have the NPN Emitter going to reset. That way if you go over voltage the system is reset and the switching stops. So bad code would just loop.