The DM invisibility command is at the heart of a DMS powers. It can be one of the three states above, off means you are visible as normal. On means that only staff might be able to see you, no players or creatures can. Room is the interesting one, this means you are visibile to anything in the same room as you, but nothing outside. A who by a player in this location will show you, one in another room will not.

The DM invisibility is not affected by detect-invisible, but you can have normal invisibility on top of the DM invis mode. In this case if a player is in the same room, you have set room mode but cast invis on yourself, then unless the player can d-i the still won't see you.

Examples :

:*invis off
Invisibility off.