Anyway to make N810 standby when it is not in use?

I don't think there is a standby mode as such. The 770 knew when you put the case on to go int standby mode but this feature is not incorporated into the 800/810. There are other power saving options on the device such as when the screen goes out and offline mode that you could play with to get the most out of the tablet when not in use. It has been said though that leaving the tablet on when not using it uses less energy than turning it off and on each use.

Thanks for the info. My 770 was dead so I got the N810. I thought it would have a similar function/setting...

Dose lock the screen and keys save battery power?

The 770's cover-on functionality is mostly identical to Lock Screen and Keys. It isn't actually a "stand-by" mode.

It does, it's called Lock Screen and Keys.

Assuming that you don't have background processes running away, yes. ARM devices use basically no power when the CPU is idle, so an idle CPU is essentially equivalent to "stand-by".