The challenge lasts 31 days.
During this month you get a free SBB-Generalabo but you can’t use your car. You can only use public transport and shared transport (for-rent cars from Mobility, for-rent scooters and bikes).
Apply here. It’s supported by the SBB so it’s real, not a scam.
Giving this a bump, because I hadn’t seen it and I received an email from SBB yesterday about the promotion.
Currently I think it’s limited to German-speaking Switzerland and some border commuter areas. The GA and use of e-bikes/scooters is free, but for Mobility one only receives a 30 CHF credit. That makes sense, given that they want people to use public transport and not cars.
It does involve registering, including providing an image of your license plate and odometer. It also requires downloading yet another app. But maybe for some people it’s worthwhile.
Here’s the FAQ page: 31 TAGE OHNE AUTO – Mach mit bei der 31DAYS Challenge! (I used the browser translator since it’s only in German, French or Italian)