You might be able to use your iPhones and Apple Watches to lock, unlock and start your cars when iOS 13.4 comes out. According to 9to5Mac, the first beta version of the mobile OS contains references to a "CarKey" API that will let you use your devices as keys for vehicles with NFC. Based on the internal files the publication saw, you won't even have to authenticate with Face ID -- you simply have to hold your device near the reader to work, even if it's out of battery.
In addition, the feature seems to have the capability to give other people access to your vehicle with their devices. You'll have to send that trusted family member or friend an invite, which you'll be able to do so via the Wallet app.
The pairing process actually starts with Apple's Wallet app, though you'll also need to have your automaker's app to finish setting up when you link a device with a car for the first time. When you place your device on top of the NFC reader, a CarKey will show up in your Wallet app. You can then add that key to an Apple Watch.
The ability to use your phone as a key is far from being a new concept, but the feature may be a welcome one if your vehicle doesn't have a digital key app. Of course, you can only hope that your car's manufacturer will work with the tech giant to implement CarKey for its vehicles.