There are door locks that can be opened with a bluetooth-enabled app on an iPhone. They work by proximity. So... If you have your phone close enough to function

There are door locks that can be opened with a bluetooth-enabled app on an iPhone. They work by proximity. So... If you have your phone close enough to function with your Apple Watch, you already have a way to lock and unlock your door without taking the phone out of your pocket. However, those same locks would be awesome if the manufacturers released a Watch app so you could manually lock and unlock the door rather than relying on proximity.