Depends on the controller I think.. And the type of pass probably.

I've forgotten my Swisspass a few times, controlled both on the train and the Geneva trams / busses.

Train :
Scenario 1 : They asked for my name and date of birth and hey presto my valid Swisspass appears on the little screen. Controller smiled and said goodbye.
Scenario 2 : Name/DoB.. Also wanted ID, gave long lecture because I had nothing (I'd forgotten my wallet) Said he should fine my and I should then claim it back minus admin charge... But didn't.

Tram :
Scenario 1 : Took my details and made a phone call, said ok, carry on.
Scenario 2 : I had my phone with me and could I login to my swisspass account and show my details., carry on.

I've been stopped ~5 times without my ticket and never fined. Be nice to the controller, agree that you were silly to forget it, smile..