California has significantly expanded a pilot program allowing citizens to get a digital driver’s license / identification card that’s accessible on their mobile phones (via 9to5Mac). The digital ID, which the California DMV is calling an “mDL” (mobile driver’s license), can be used for things like getting through airport security or proving your age when buying alcohol.

The free pilot is now open to 1.5 million participants, according to the DMV’s website for the program. You can sign up for it by downloading the “CA DMV Wallet” app on iOS and Android.

If you choose to sign up for the state’s digital IDs, there’s a few caveats to be aware of. The DMV stresses that you’ll still need to carry your physical ID or driver’s license given that “law enforcement, state government agencies, and businesses aren’t yet accepting the mDL.” Only some airports and a handful of retail locations support them. The DMV promises that the app “does not permanently store your personal data,” but it does keep your phone number and an “encrypted photo of your DL/ID card.”

And California isn’t letting citizens add a digital ID to iOS or Android’s native wallets; instead, you have to use California’s dedicated app. “At this time mDL is not available for Apple or Google wallets,” the DMV says. “However, additional platforms will be available in the future.”

California governor Gavin Newsom suggested at the beginning of this year that was getting ready to launch digital driver’s licenses. A few weeks ago, Los Angeles’ NBC 4 reported that the pilot had more than 2,000 participants and that the pool would expand soon.