Time Spent in each room

Thanks for this Stachu, this definately guided me in the right direction. 

I've done the following, I've said in one calculated column, where Motion[Room] <> CurrentRoom and another where Motion[Room] = CurrentRoom - then used an IF statement to return the relevant value. I can then just sum the values as required and I have question 1 answered.  Let me know if there is a cleaner way of doing this. 

Travel Time = 
VAR CurrentRoom = Motion[Room]
VAR CurrentLocation = Motion[Location]
VAR CurrentDate = Motion[Date]
VAR CurrentTimeStamp = Motion[DateTime]
VAR PreviousTimeStamp =
    CALCULATE (
        MAX ( Motion[DateTime] ),
        ALL ( Motion ),
        Motion[DateTime] < CurrentTimeStamp
    )
VAR PreviousRoomTimeStamp =
    CALCULATE (
        MAX ( Motion[DateTime] ),
        FILTER (
            ALL ( Motion ),
            Motion[DateTime] = PreviousTimeStamp
                && Motion[Location] = CurrentLocation
                && Motion[Room] = CurrentRoom
        )
    )
RETURN
    IF (
        PreviousRoomTimeStamp <> BLANK (),
        CurrentTimeStamp - PreviousRoomTimeStamp
    )

Travel Time 2 = 
VAR CurrentRoom = Motion[Room]
VAR CurrentLocation = Motion[Location]
VAR CurrentDate = Motion[Date]
VAR CurrentTimeStamp = Motion[DateTime]
VAR PreviousTimeStamp =
    CALCULATE (
        MAX ( Motion[DateTime] ),
        ALL ( Motion ),
        Motion[DateTime] < CurrentTimeStamp
    )
VAR PreviousRoomTimeStamp =
    CALCULATE (
        MAX ( Motion[DateTime] ),
        FILTER (
            ALL ( Motion ),
            Motion[DateTime] = PreviousTimeStamp
                && Motion[Location] = CurrentLocation
                && Motion[Room] <> CurrentRoom
        )
    )
RETURN
    IF (
        PreviousRoomTimeStamp <> BLANK (),
        CurrentTimeStamp - PreviousRoomTimeStamp
    )

And finally...

Time Spent =
IF (
    FIRSTDATE ( Motion[Date] ) && ISBLANK ( Motion[Travel Time] )
        && ISBLANK ( Motion[Travel Time 2] ),
    Motion[Time(no secs)],
    IF (
        ISBLANK ( Motion[Travel Time] ),
        Motion[Travel Time 2],
        Motion[Travel Time]
    )
)

And then the count of motion censor triggers

Activity Count =
CALCULATE (
    COUNT ( Motion[Room] ),
    ALLEXCEPT ( Motion, Motion[Date], Motion[Location], Motion[Room] )
)

Any revisions will be appreciated, else I am a happy chappie :-)

Thanks again!!