On how many iPhones and Apple Watches can a hotel room key in Apple Wallet be activated?

You may add room keys to Apple Wallet on one iPhone and one paired Apple Watch per iCloud account.

If you need to switch iPhone, you may add a room key to a second iPhone. When the key is activated on the new iPhone, the room key will be automatically removed from the previous device.

If you need to switch Apple Watch, you may add a room key to a second paired watch. When the key is activated on the new iPhone, the room key will be automatically removed from the previous device.