[ixm7]

When my partner is timed out and replaced with a Robot, there is no beep or alert.
So I'm not aware of the switch. I keep playing assuming out bidding system is in effect.
Not good...

[pescetom]

There is also the opposite problem. A few days ago a TD invited me to play with a robot in his tournament and I accepted: but at a certain point I noticed that my artificial bid had not self-explained and looking for a reason I saw that robot had become an unknown human (not what I was offered or wanted). I quickly explained the agreement but opponents were still sour that LHO had already called.

So both giving a clear robot/human substitution message and advising innocent subs that their proposed partner is a human and not the robot mentioned would be appropriate.

[0 carbon]

As a TD, I always "welcome" human subs.
-- tom

[0 carbon]

Instead of, or in addition to, an alert sound, when a player changes, you could flash the player ID, eg, black on white, white on black, a couple of times.