BOD Example and ATTiny-1604?

I have an application that requires the Arduino (probably an ATTiny 1604) to be always powered, but go into low-power sleep mode most of the time. I need to KNOW if power is ever lost. I've been looking for a good, clear example of using the BOD, but have come up mostly empty. Does anyone know of a good BOD example?

Also, is there currently Arduino support for the newer AVRs, in particular the ATTiny 1604? At ~$0.60 each even in one-sies, this part is very attractive.

Ray L.