[Coco] Detecting when CoCo is turned OFF

[Salvador Garcia]

Hello all!
I am pondering on designing an Arduino based board to receive serial data coming from the CoCo's bit banger port. I would like for the Arduino board to do something when the CoCo is powered off and am thinking of ways to detect this event.
The serial connection has four lines: CD, Gnd, Tx and Rx. I don;t see using any of these for this purpose, unless I missed something.
Another possible solution is for the Arduino to have a connector that goes to the joystick port and monitor its Vcc line, but I really hate taking up a port for this, plus this solution seems clunky.
Does anyone have any ideas? Maybe I am not thinking of something obvious. Thanks! Salvador